rs ins 

.J ?3 



TS 1175 
.S83 
Copy 1 



BULLETIN OF THE 




No. 80 



Contribution from the Forest Service, Henry S. Graves, Forester. 
August 31, 1914. 

(PROFESSIONAL PAPER.) 




EFFECTS OF VARYING CERTAIN COOKING CONDI- 
TIONS IN PRODUCING SODA PULP FROM ASPEN. 

By Henry E. Surface, 
Engineer in Forest Products, Forest Products Laboratory. 

PURPOSE OF EXPERIMENTS. 

At the present time practically all of the soft, easy-bleaching pulps 
used for the manufacture of high-class book, magazine, general print- 
ing, and the cheaper writing papers are made by the soda process. 
In England such pulps are produced from esparto (alfa, or Spanish 
grass) ; in America, from the poplars and similar woods. Although 
the soda process of wood-pulp manufacture is not employed commer- 
cially to so great an extent in America as the sulphite and mechan- 
ical processes, it is remarkably well adapted for producing pulp fibers 
from any kind of wood or other fibrous vegetable material, no matter 
how resistant to chemical attack it may be. For this reason it is 
much used in the experimental work of the Forest Service. 

To insure that a wood has been subjected to the most favorable 
cooking conditions it is necessary to cook it under many different 
conditions produced by varying such factors as the amount and con- 
centration of the cooking chemical and the duration and temperature 
of cooking. While the general effect of using greater or less severitv 
of cooking is well recognized in mill practice, there has been almost 
no available information on the quantitative effects of the individual 
factors concerned nor on the limitations within which such effects 
are exerted. Such meager information as may be found in the litera- 
ture is widely scattered and is not strictly applicable to manufactur- 
ing conditions. Notwithstanding modern improvements and the 
general tendency toward more efficient operations in commercial 
plants, the most economical production apparently is not being 
attained by all of the soda-pulp mills. This is indicated by the fact 
that some of them are using from 10 to 20 per cent more pulp wood, 
from 50 to 100 per cent more chemicals, and from 10 to 40 per cent 

1 This paper presents detailed information of value in experimental work in the laboratory and in pro- 
moting the efficiency of commercial paper-making plants employing the soda process. 

31091°— Bull. 80—14 1 . 

, raph 

■ 



2 BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 

more steam, and require much Larger plants and more labor for the 
same tonnage output per day than others making similar products. 
It was to sccuro and make available detailed information which would 
both facilitate other experimental work in the laboratory and promote 
the efficiency of commercial plants employing the soda process that 
the series of tests discussed in this bulletin was undertaken. They 
were carried out at the Forest Products Laborato^ maintained by 
the Forest Service at Madison, Wis., in cooperation with the Univer- 
sity of Wisconsin. 

The report of the experimental work is prefaced by a short descrip- 
tion of the soda process and a review of previous investigations. 
Some general comments on aspen as a raw material for soda pulp and 
on the pulp itself will be found in the appendix, pages 41-47. This 
species of poplar was selected as the test material because it is the 
most important soda pulpwood. The information secured, however, 
is of much value also in connection with the cooking of other woods. 

THE SODA PROCESS AND ITS APPLICATION. 

What is here referred to as the soda process may be considered as 
a modification of the old Watt and Burgess process, first practiced 
in 1853, 1 and probably the oldest commercial method for producing 
chemical pulp from wood. It originally consisted in digesting suit- 
ably prepared wood in a large boiler with a strong solution of caustic 
soda under a pressure of about 90 pounds per square inch for 10 or 
12 hours. The wood was then washed to remove the alkali and 
treated with chlorine gas or an oxygenous compound of chlorine. 
The partially digested wood was then washed to free it from the 
hydrochloric acid formed and again treated with a small quantity 
of caustic soda solution. The pulp so produced was then washed, 
bleached, and beaten in a beating engine, after which it was ready 
for the paper machine. The modification of this process as employed 
at the present time in the United States dispenses with the interme- 
diate digestion treatment with chlorine compounds. Different cook- 
ing conditions also are used, the details of which, together with a 
brief description of the manner of preparing the wood, are given 
below. 

PREPARATION OF THE WOOD. 

While a few mills cook their wood unbarked or only partly barked, 
the general practice is to remove even the live inner bark. 2 The 

• Charles Watt and Hugh Burgess secured a United stales patent on this process in. 1854. It was devel- 
oped further and modified by Jnilloii in France (1855), by Houghton in England (1857), and by Afbcrt 
lingerer, to whom a British (latent was issued (1872). Further modifications gradually resulted from its 
commercial application. 

2 The harking loss amounts to about one-fifth of the weight of unbarked logs. The losses in the ease or 
logs from 31 trees used in these experiments varied from 18 to 20 per cent, which checks quite well with 
Ziegelmeyer's figure of 19.5 per cenl on European aspen. (See Stevens, Paper Mill Chemist, p. 150, 1908.) 
Aside from the convenience and ease of barking in Che woods, the saving of freight Is considerable when the 
wood is transported to the mills by railroad, and since the barked wood dries out rapidly an additional 
advantage is secured by the loss of weight in seasoning. A cord of green aspen (about 50 percent water) 
weighs about 1,900 pounds more than the same wood, air dry (about 15 percent water). 

SEP If 1914 



PRODUCING SODA PULP FROM ASPEN". 



<"- 



barked or peeled wood is then cut diagonally with the grain into 
slices or chips about one-half to three-fourths inch thick by means 
of a machine called a "chipper." These pieces are then further 
broken up by means of a disintegrator, or "shredder," and the 
resulting chips are conveyed to storage bins, usually above the 
digesters. An intermediate screening operation to remove dust 
and dirt and to secure uniform chips is sometimes given them. 

On account of the strong solvent power of the cooking liquors used 
in the soda process it is not necessary to remove completely the knots 
or decayed portions of the wood. At some mills, however, the 
chips before being stored are sorted into different grades from which 
different qualities of pulp are produced. In the case of peeled wood, 
delivered as such to the mill, the outer shavings, if the wood is rc- 
cleaned, are kept by themselves and converted into a lower-grade 
product. In some of the older mills the knots were removed from the 
peeled logs with a boring machine; and later the chips were picked 
over by hand. Such procedures, however, have now been practically 
abandoned in America. 

THE COOKING PROCEDURE. 

The digesters used in soda-pulp making are either rotary or sta- 
tionary, and may be either cylindrical or spherical in shape. The 
present tendency in new installations is towards stationary, vertical, 
cylindrical digesters heated by live steam which enters at the bottom 
of the digester in such a manner as to carry the cooking liquor through 
a pipe to the top of the vessel and spray it over the chips. This 
insures good circulation. The chips and cooking liquors are charged 
through a manhole at the top of the digester, the bottom of which is 
provided with a "blow-off" pipe and valve for discharging the pulp 
after the cooking is complete. Such digesters are from 15 to 50 feet 
high by from 4 to 9 feet in diameter. The larger sizes have been 
lately introduced; in the past the most common size held about one 
cord of wood and was 16 feet high by 5 feet in diameter. At the time 
of the 1905 census the average American digester produced about 
1 ton of pulp per cook, and the total combined capacity of the 208 
soda digesters in operation then was 222 tons of pulp per cook. 

As soon as the charging of chips and caustic soda cooking liquors 
is complete, steam is turned into the digester until a certain cooking 
pressure or temperature is reached. This temperature varies at 
different mills, but one corresponding to 110 pounds steam pres- 
sure per square inch is probably the most common at present. The 
pressure is continued from three to eight hours or more. 1 

WASHING OF PULPS AND RECOVERY OF COOKING CHEMICALS. 

After the digestion process is completed the pulp in the digester 
is generally forced out under pressure or "blown" through a pipe 

1 The detailed cooking conditions employed at various miTls are shown in the appendix, Tables 16 and 17. 



Adr M-M 



4 BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 

connected with the bottom of the digester into a "blowpit" or 
"balloon;" whence it is transferred to large washing pans. Here it 
is drained as free as possible from the strong spent cooking liquors, 
called "black liquors/' and washed thoroughly, first with hot, weak, 
black liquors from the last washings of previous cooks, and lastly 
with fresh hot water. The first drainings and washings which con- 
tain the greater part of the alkali cooking chemicals are run to evap- 
orators, concentrated , and later calcined in furnaces. The burned ash, 
called "black ash," is leached with water, and the alkali in the form 
of sodium carbonate is dissolved. The resulting solution is treated 
with quicklime (CaO), which changes the carbonate into caustic soda. 
Modern practice recovers from 88 to 92 pe,r cent of the alkali charged 
into the digesters. By properly controlling the strength of the black 
ash solution and mixing various strengths of recausticized solutions, 
a caustic soda liquor of the desired strength for cooking is prepared. 1 

TREATMENTS GIVEN THE SODA PULP. 

After the pulp has been thoroughly washed it is diluted with a large 
amount of water and screened to remove uncooked portions. This 
is accomplished by either Hat plate, diaphragm screens, or by such 
screens in conjunction with centrifugal ones. In the case of aspen 
or poplar the greater proportion of the water in the pulp is then 
removed by means of "slushers," "fcltless wet machines," or 
"deckers." The pulp is then treated in a suitable vessel with bleach- 
ing-powder solution and afterwards thoroughly washed. Very little 
aspen or poplar pulp is left in the unbleached state, but is usually 
bleached immediately after it is screened. Those mills making both 
pulp and paper generally carry the bleached wet pulp directly 
through the subsequent paper-making operations; but if the pulp 
is to be sold or stored it is simply run over a paper machine into rolls 
of dry pulp (about 10 per cent water). 

PREVIOUS INVESTIGATIONS. 

The treatises by Cross and Bcvan 2 and by Schwalbe 3 and the 
recent experiments 4 by Viewig, Miller-Moskan, Miller, Schwalbe, and 
Schwalbe and Robinoff give much information on the nature of the 
chemical reactions which take place between caustic soda and cellu- 
lose under various conditions, and on the formation of decomposition, 
mercerization, and other similar products from cellulose. 

1 A few mills still cling to the older practice of not recovering the alkali from the black liquors. Such mills 
buy the alkali for cooking in the form of caustic soda (NaOB I. The cooking solution is produced by dis- 
solving in water a sufficient quanl ily of Iho can si lc to give 8 SOlul Ion of Hie desired strength. The black 
liquors are run to w asie, and, although the consumpt ion of cooking chemicals is very high, the mills seem 
to operate at a prolit. 

» Cellulose, 1903. Also Researches on Cellulose, 1895 1900; 1900 1905; 1905-1910. 

« Die ('hemic der Cellulose. 1910 1912. 

1 For specific literature references see bibliography in appendix. 



PRODUCING SODA PULP FROM ASPEN. 5 

While the manufacturer of paper pulp is interested in these chemical 
investigations they do not give him much practical information on the 
interrelation of the various cooking conditions winch he employs and 
the effect of their modifications on the yield and quality of the pulp. 

An article published by Tauss 1 in 1889, dealing with the effects of 
water alone on cellulose-containing materials, is of interest in connec- 
tion with the Forest Service tests because the "yield" or residue with 
zero caustic soda assists in determining the curve for the effect of 
amount of caustic soda on the yield of crude pulp (fig. 4). Tauss's 
experiments showed (Table 1) that a very appreciable amount of 
solids can be extracted from wood and from cellulose by boiling in 
water, especially at high pressures. In 1890 the same author 2 pub- 
lished the results of investigations in which caustic-soda solutions were 
employed in the place of water alone. The experiments with caustic 
soda were made partly with solutions of a concentration employed in 
commercial practice, partly with more concentrated, and partly with 
more dilute solutions. 3 The calculated residues (Table 1) afford some 
interesting comparisons with the Forest Service yield data. 

In 1907 De Cew 4 published a technical article dealing with the func- 
tion of the soda process in the production of wood cellulose. Although 
no data are cited to substantiate his conclusions, he makes the fol- 
lowing statements : 

The results obtained with this process depend very largely upon the accuracy with 
which it is carried out. The action of caustic soda is one of hydrolysis, in which the 
woody molecule is gradually broken down with the formation of acid products which 
combine with and neutralize the alkali, leaving the cellulose in the form of isolated 
fibers. Now, if sufficient alkali were used and the cooking action continued, the entire 
fiber would finally be dissolved, although the more resistant celluloses would be the 
last to disappear. It is, therefore, necessary in order to bring into solution only the 
lignified portion of the wood to add just sufficient alkali for this purpose. 

This is almost entirely neutralized by the acid products formed from the lignocellu- 
lose, and thus very little free alkali is left in the liquor to attack the rest of the fiber, 
which should be almost pure cellulose. At first the alkali is very active and a rapid 
combination takes place, but the rate of reaction becomes continually slower as the 
free alkali grows less and the resistance increases. There are also such varying con- 
ditions as to causticity, pressure, circulation, and time of cooking, which are of con- 
siderable importance in the process, for some makers are obtaining from 1-200 pounds 
of fiber per cord more than others in treating the same kind of wood. 

' Dingl. Polyt. J., pp. 276-285, vol. 273, 1889; Jour. Soc. Chem. Ind., p. 913, vol. 8, 1889. 

2 Ibid., pp. 411-428, vol. 276, 1890; Jr. Soc. Chem. Ind., p. 883, vol. 9, 1890. 

• See footnote, p. 16. 

«Jour. Soc. Chem. Ind., pp. 561-363, vol. 26, 1907; Chemical Abstracts, p. 319, 1908. 



BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 



s 


o 


-« 


-Q 




a 


i 


o 






-a 




s 


01 



"fe 



^ 

^ 



— «■ 

£3 






*3 



i?ii 



r~ oo -<r o c^*^^o 






to CD CO "'P 

00 lO -^ CO 



3 i. « H i 



JO, 
o at. 



£S 



^8 



ft, 5 



.cn — coo r-aiioo to — < m n 

bvHOOO IONIAN U)hO« 

lSccmno coooaicd -*r cd ^ oo 

^ul-UOOOO "OtOQOS CD CO I- O 



' r^ r- t ^* 



.§8< 

o 35 o » 



!S§S 



fi 3 
a.— 
t^ o 






Vfet 



ooV-OOOO OQOO 000< 



■oooo oooo ooop 

trlMMCN — -HrHCM — r-l « <N 



£ a 
a* 



h 


V 


_ 




2 






o 


X! 


~ 




— 


; J 



09 










- 


-. 


- 

o 


- 
-1 


at 


s 


o> 




< 


99 




y 










- 


c 




at 




A 


a 




■^ 


T» 


B B 




Jj 


B 


rn 






: 


O 


A 










X 










« 





B S 

• d **" 

*c3 -t- 3 B 

.S . a o 

So >- 
"38 -S 
SbSS 

J?ES£ 

H o a B* 



t- t! s .3 

_ 3ft" a 
o-3d.2 w 



-2 H at c3 

go -° 



» ts — S 5 ^ — >- 

_ c: ,. c t; <« oa; 

o-..ii c3-g « • -2 

•3 d w ci £ ;- h' 

S-ISSg^J IS 
ialllll 






.a-3cao^ c o 



"3 o 



SS'SSaa-S.! 

3 BTJ a,© ®-B w g 

Is 5 



PK0DUCING SODA PULP FROM ASPEN. 7 

In regard to the time required for cooking there is a wide difference in practice. 
However, the most improved plants are now able to effect the complete resolution of 
the wood in a very short time. In fact, any of the deciduous woods can now be 
reduced in about four hours. With the improvements in the methods of cooking that 
have been developed, which enable us to get about twice the work out of a digester 
that was formerly obtained, a number of special advantages have been found to be the 
result of these quick cooks. The shorter the time the alkali is in contact with the 
cellulose, the higher is the yield obtained and the sounder and stronger is the fiber. 
If all of the cellulose is freed from the lignin at practically the same time, the free 
alkali will have very little time to react on the weaker celluloses and the fibers will not 
be broken nor the points and serrations dissolved. Moreover, the fibers from the short 
cook are not hard to bleach, because the character of the cellulose is uniform. Under 
conditions of complete saturation with the right proportion of alkali, the lignocellu- 
loses can be almost instantly dissolved by subjecting the material to the temperature 
and pressure that is ordinarily used for cooking the fiber. The writer has performed 
this experiment on a laboratory scale, and the fiber obtained so closely resembled the 
actual structure of the woody cell that hardly any cellulose could have been dis- 
solved. 

Clapper/ton/ in 1907, in writing about the soda process, says: 
It is the necessity for employing such high temperatures and pressures (90 pounds 
per square inch) that constitutes the serious drawback to the alkali process as under 
the conditions of boiling the strong caustic soda acts on the cellulose, impairing the 
strength and reducing the yield. 2 The reason why such conditions are necessary is 
that the soluble acid bodies resolved by the caustic become so oxidized and con- 
densed that they counteract and weaken the reducing action of the soda, and in order 
to equalize then- resistance higher temperatures and pressures have to be employed. 

Beveridge 3 recently published the results of some of his experi- 
ments on the effects of varying the cooking conditions in the produc- 
tion of esparto pulp. He says: 

The treatment of esparto by the soda method is typical of the preparation of paper 
pulp from nearly all fiber-yielding plants, such as bamboo, straw, wood, etc. The 
isolation of cellulose is brought about by digesting the prepared plant in an alkaline 
solution, having for its base caustic soda, at variable temperatures and under variable 
lengths of time. The chemical reaction which takes place during this digesting proc- 
ess is not known; that is to say, has not been isolated because of the complicated char- 
acter of the encrusting substances surrounding the fiber in the plant. The caustic 
soda in aqueous solution forms soluble compounds with these encrusting bodies and 
dissolves any silica which forms a part of the plant's structure, so that by subsequent 
draining, washing, and bleaching the liberated cellulose is obtained in a compara- 
tively pure state. Cellulose from whatever source it is obtained is, however, soluble 
in aqueous solutions of caustic soda. Moreover, the solvent action of the caustic is 
accelerated by heat and by the length of time (within limits) in which the two bodies 
are heated together. It is therefore apparent that if the maximum yield of cellulose 
is desired when using this method due regard must be paid to the laws regulating the 
yield. These laws may be expressed thus: The yield of cellulose obtained from any 
plant by the caustic-soda method depends upon: 

(1) The proportion of caustic soda (NaOH) used per unit weight of plant; 

(2) The temperature employed; and 

(3) The length of time the digesting operation is continued. 

1 Practical Papermakiiig, p. 33, 2d ed., 1907. 

2 In modern commercial practice even higher temperatures and pressures are employed, and the results 
of the Forest Service tests do not corroborate Clapperton's statements as to. the undesirable effects from using 
them. 

» Papermaker's 1'ocketbook, p. 72, 2d ed., 1911. See also Sindall, Manufacture of Paper, p. 77, 190S. 



8 



BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 



If any one of these conditions be altered and the other two kept constant, the yield 
varies inversely as the altered condition. Thus, in the case of esparto, the author 
performed a series of experiments in which the proportion of caustic to unit weight of 
esparto was varied, whilst the temperature and duration of time of digesting were both 
kept constant with the following results (Table 2). 

Tahle 2. — Experiments regarding yield of air-dry bleached pulp from Oran esparto. 



No. of ex- 
perimenl . 


Esparto, 
weight 
taken. 


Soda liquor. 


Conditions of boiling. 


Weight of 
air-dry 
pulp: 


Dry pulp 
on dry 
esparto. 


li leaching 
powder. 


Volume. 


Na 2 0. 


Time. 


T 7^ ra j Pressure. 


1 


arums. 
200 
200 

L'IMI 


Cc. 
800 
800 

SIM) 


Per cent. 
1.58 
2. 13 
2.69 


Hours. 

3 
3 
3 


"C. 

142 

142 
142 


Lbs. 
55 
55 
55 


Grams. 
87.30 
80.67 
72. 00 


Per cent. 
43. 91 
40. 55 
3d. 20 


Per cent. 
29.5 


2 


IS. 5 


3... 


10.5 







Note, — The different dials were made in wrought-iron tubes fitted with screw caps, all Diree being 
healed together ill an oil bath for three hours at a temperature of 302° F. (55 pounds aboye atmosphere). 

The following is taken direct from Cross, Bevan, and Sindall's ' 
resume of Beveridge's experimental results, which include the data 
quoted in Table 2 and others: 

lie made three sets of trials, as follows: 

Constant conditions. Variable. 

1. Time and strength of caustic. Pressure varied. 

2. Pressure and time. Strength of caustic varied. 

3. Pressure and strength of caustic. Time varied. 
The results were: 

1. Increase of pressure resulted in a diminution of yield, the quantity of pulp 
obtained being reduced considerably. 

2. Excess of caustic soda caused rapid diminution in the yield of cellulose. 

3. Gradual exhaustion of the caustic soda by prolonged digestion prevented such 
serious diminution of yield. 

The discussions and experimental results which have been quoted 
show in a general way the effects of varying some of the fundamental 
cooking conditions in the soda process. None of the experiments 
cited are directly comparable to commercial practice in this country, 
because the testing conditions were not sufficiently representative of 
manufacturing conditions, and, in the case of Beveridge's experi- 
ments, because esparto — a grass, or pectocellulose — was used as the 
test material. Moreover, the effects of the cooking conditions 
employed were not studied in as great detail as seemed desirable. 
The experiments show very clearly, however, that improper cooking 
conditions are wasteful or inefficient, and indicate the need for com- 
plete experimental data on which improvements in commercial 
practice may be based. 

i Wood Pulp and Its I'scs, p. 1!L>, 1911. 



PRODUCING SODA PULP FROM ASPEN". 9 

METHOD OF CONDUCTING EXPERIMENTS. 

SCOPE AND PLAN OF TESTS. 

Aside from the character of a wood or other material prepared for 
cooking, the principal cooking conditions affecting yields and proper- 
ties of pulps, consumption of cooking chemicals, and the general 
efficiency and costs of the cooking operations are indicated under 
the following general headings: 

(1) Preliminary treatments which may in some cases be given the prepared 

chips. This includes such treatments as preliminary pressure, vacuum, or 
steaming. 

(2) Character of the cooking apparatus, including size, shape, and construction 

of the digester; manner of heating, whether by saturated or superheated 
steam turned directly into the digester, or by the use of steam jackets or 
flue gases; also the degree and kind of mechanical agitation employed, 
if any. 

(3) Proportions of the charges. This covers the amounts of wood and chemicals; 

also the amounts of water present in the wood and the original cooking solu- 
tions together with the water condensing in the charges from steam used in 
cooking. 

(4) Character of the cooking liquors when charged. Such items as causticity, 

initial temperature, impurities, and concentration are important. 

(5) Duration of the cooking treatment. The treatment is in three periods — (a) a 

period of increasing temperature; (b) a period at maximum temperature; 
and (c) in some cases, a period of decreasing temperature. 

(6) Pressures and temperatures. This considers the pressures and temperatures 

of the digester contents at different stages of cooking; also the tempera- 
ture of the digester room (as affecting radiation and condensation). 

(7) Manner of admitting steam, "relieving," and "blowing" the digester. 

Since the effects of the variable cooking conditions may be modi- 
fied by the treatments given the pulps after leaving the digester — 
such as leaching or washing, screening and bleaching — these treat- 
ments must also be taken into account, for it is not possible to de- 
termine all the important effects of the cooking treatments until the 
finished pulps have been prepared. 

The many factors are more or less interdependent, and any change 
in one results in unavoidable changes in others. Four of the more 
fundamental of these factors have been investigated in the Forest 
Service experiments. They are: 

(1) Amount of caustic soda charged per pound of wood. 

(2) Duration of cooking at maximum temperature. 

(3) Maximum temperature (pressure) of cooking. 

(4) Initial concentration of the cooking chemicals. 

The effect of these four factors upon the yield and properties of the 

pulp and the consumption of cooking chemicals were determined. 1 

1 — 

1 The purely chemical aspect of the cooking action has not been given special consideration. The effect 
of the caustic soda cooking liquors under the conditions employed in pulp making is recognized as a hydro- 
lytic action in which the caustic soda extends the limits of hydrolysis. This subject has been given care- 
ful attention by Cross and Bevan, Schwalbe, De Cew, and others as indicated in previous references. The 
effects of the cooking conditions on the recovery of soda also have been given no consideration except in a 
very cursory manner. The laboratory facilities did not permit this important subject to be studied at the 
time of the experiments. 



10 



BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 



The tests fall naturally into four groups; in each group all the condi- 
tions were held as nearly constant as possible except the factor under 
investigation, which was varied in successive tests or "cooks" accord- 
ing to a definite plan. The plan of the tests is shown in Table 3. In 
addition to the factors mentioned in this table all other factors under 
control were so far as possible held constant. Those for which values 
were specified are the following: 

Amount of chips for each charge, 40 pounds bone-dry weight. 

Dryness of chips, air dry. 

Causticity of cooking liquors, 95-9S per cent. 

Temperature of charging cooking liquor, 22° ('. (72° F.) 

Temperature of digester room, 22° C. (72° F.) 

Duration of cooking before maximum pressure is reached, 1 hour. 

Duration of cooling and relieving digester before blowing, 5-10 minutes. 

Blowing pressure, 'A0 pounds per square inch. 

Table 3. — Plan of cooking experiments. 





Num- 
ber of 
tests. 




Cooking conditions 


under investigation. 




Test 
group. 


Initial concentration 
<>i caustic soda in 
digester Liquors. 1 


Amount of caustic 
soda per 100 
pounds of wood. 1 


Maximum cooking 
temperature 
(equivalent steam 
pressure). 


Duration of cooking 
at maximum pres- 
sure or tempera- 
ture. 


I. 

IF. 

III. 


6 
6 

u 

4 


I onstani mi grams 
per liter. 

Same as < iroup I 

.do 


Variable — from 15 

to -ID pounds in 
steps of 5 pounds 
each. 

Cm/stunt— 25 pounds 
(value selected 
from Group 1 tests 
as most satisfac- 
tory for later tests). 

Same as Group II... 

.do 


C o ii s t a n t— 1 
pounds per square 
inch. 

Same as Group I 

Variable— from 70 to 

120 pounds per 
square inch in 
steps of 10 pounds 
each. 
Cons tan t—\ 
pounds per square 
inch (value se- 
lected from Group 
III tests as most. 
satisfactory for 
later tests). 


Constant— % hours. 

]'ti liable — from 1 to 
11 hours in steps 
of 2 hours each. 

Cons/ant — 7 hours 


IV. 


Variable — from Hi) 
to 50 grams per 
liter in steps of 20 
grams each. 


(value selected 
from Group II tests 
as most satisfac- 
tory for later tests). 
Same as Group III. 









) In commercial practice it is customary to vary the amount of chemical used and its initial concentra- 
tion both at the same time when attempting to change the severity of the cooking due to these factors. 
This results in the volume of the cooking liquors being kept approximately the same, which is a desirable 
feature. In these tests, however, it was the intention to find out the effects of each factor separately. 

TESTING PROCEDURE. 

The apparatus employed in cooking is shown in figure 1. Figure 
2 shows diagrammatically the course of the material through the 
various stages of treatment and testing, and in this way the relation 
of one part of the procedure to another is made clear. 

After the amount of moisture in the chips had been ascertained 
by means of sample A, the charge was weighed out and put into the 
digester. Caustic soda solution, of the desired concentration and 
volume, had been prepared by diluting the necessary quantity of 
analyzed stock solution (sample B) with water. It was then heated 



PRODUCING SODA PULP FROM ASPEN. 



11 



to the charging temperature and run into the digester, and the cook- 
ing operation was begun by permitting live steam to enter at the 
bottom. 

During the cooking, observations were made at 15-minute intervals 
of (1) digester temperature, (2) digester pressure, (3) steam pressure 
at digester inlet, and (4) room temperature. The volume of liquor 




in the digester was also observed, but at hourly intervals. These 
observations were recorded, and a graphic "log of cook" was made 
at the same time, an example of winch is shown in figure 3. If at 
any time the digester temperatures and pressures as observed on the 
thermometer and pressure gauge did not agree when compared by 
means of pressure-temperature tables for saturated steam, the excess 
of pressure was relieved; such a condition occurred as a rule only dur- 



12 



BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 



ing the first hour of cooking. The room temperature and the pres- 
sure of steam at digester inlet were kept as near constant as possible 
for all the tests, so that all conditions affecting condensation, aside 
from the cooking operation itself, would he uniform. For the same 



1 STEAM MAIN~] 1 ALKALI STORAGE TANK~| 1 STORAGE CANS 1 1 WATER MAIN 1 

ST^AM CAUSTIC SODA LIQUOR CHIPS WATER 



1 STEAM SEPARATOR 



f LIQUOR PREHEATER 1 

CAUSTIC SODA AMD WATER 



SCALES 

1 



DIGESTER 



RELIEF LIQUOR 



BLOW PIT 



■AW 



BLACK LIQUOR 



BLACK LIQUOR 



LEACHED PULP 



BLACK LIQUOR TANK 

! 

BLACK UQUOR 



PRESS 



DRAWINGS 




r^ 

PRESSED PULP 

I shredder" 

SHREDDED PULP 




SAMPLE D 



CRUDE PULP AND WATER 

CENTRIFUGAL PUMP 

CRUDE PULP AHO WATER 

STOCK TANK 

CRUDE PULp! AND WATER 



SCREEN 



SCREENINGS AND WATER 

WATER EXTRACTOR 



SCREENED PULP AND WATER 



WATER EXTRACTOR 



SCREENINGS 

SCALES 

SCREENINQS 



WATER WATER 



WASTE 



SEWER 




PULP AND WATER 

STUFF 'cHESf 

PULP AND WATER 

1 ' MACHINE SCREEN"! 

PULP AND WATER DIRT AND SCREENINGS 



PAPER MACHINE 



WASTE 



WATER 



DRY PULP IN ROLLS 
UNBLEACHED 




Fig. 2.— Flow sheet , showing course of material through the various stages ut treatment and testing. 

reason, steam of approximately the same moisture content was used 
in all tests. 

During the first hour of cooking the digester pressure and tempera- 
ture were brought, at a uniform rate, up to the maximum to be 



PRODUCING SODA PULP FHOM ASPEN. 



13 



employed, and were held constant at this value during the remainder 
of the cook. At the end of the cooking period the top relief vent 
was opened and the digester pressure quickly "relieved" until 
"blowing pressure" was reached, when the vent was closed, the two 
blow-off valves were opened, and the digester was emptied under 
blowing pressure with 
the assistance of a steam 
ejector in the blow-off 
line. 

The pulp was caught 
in the blow pit, where 
it was washed with three 
or more 50-gallon appli- 
cations of hot water. 
After the blowing and 
after each successive 
washing the pulp was 
allowed to drain, and the 
drainings were pumped 
to the black-liquor stor- 
age tank. The washing 
operations were contin- 
ued until the last drain- 
ings were of a specific 
gravity lower than 1 .003 
at 22° C. Inasmuch as 
the top relief pipe emp- 
tied into the blow pit, it 
was possible to collect 
the small amount of 
relief liquors, together 
with the black liquors, 
in the storage tank, 
where the volume of the 
whole was read off on 
the graduated tank 
gauge. A sample of this 
(sample C) was secured for analysis, and the amount and character 
of the recovered chemicals determined. (Fig. 2.) 

After the last washing the crude pulp in the blow pit was drained 
as dry as possible and, by means of scoops, removed to a strong linen 
bag inclosed in a perforated metal cylinder. The pulp in this form 
was then placed under a 70-ton, knuckle-joint, power press. After 
being pressed to about 30 per cent bone dry the pulp was next 




Fig. 3.— Typical graphic log of cook. (Cook 24.) 



1 1 BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 

"opened up" in a swing-hammer shredder running at low speed 
and without a cage, so that the largest lumps after shredding were 
about hazelnut size. Tliis was done to facilitate sampling and 
increase the accuracy of the dry-weight determinations. The 
shredded pulp was weighed and sampled (sample D) for determin- 
ing the dry weight. It was then mixed with water and further' 
opened up in a 25-pound Hollander-style beater, with the roll well 
off the bedplate so that no real beating could take place, and was 
pumped from the heater to a 200-gallon stock tank at the head of the 
screening system, where it was diluted with water to a known volume. 
This mixture was then screened by means of a 6-plato diaphragm 
screen with slots 0.009 inch wide. The screenings which went over 
the plates were then collected, weighed, and sampled (sample E), as 
described for the crude pulp. The screened, unbleached pulp which 
went through the screen slots, mixed with a large amount of wat< r, 
was run to a water extractor and concentrated. Afterwards it was 
pumped to the paper machine stuff chest, made up to a known volume 
with water, pumped to the machine screen (diaphragm type, 0.012 inch 
slots), and run out on a 15-inch Fourdrinier paper machine (see PL I), 
into a sheet 10 inches wide by about 0.010-0.011 inch thick. The 
rolls of the screened, unbleached pulp thus secured were stored await- 
ing the tests to determine its properties for which samples G to K 
were taken. Where the screenings were so large in amount as to 
preclude accuracy of sampling the crude unscreened pulp, such pulp 
was screened without the preliminary pressing, shredding, etc., and 
the screened pulp was collected on a 70-mesh sieve, pressed, shredded, 
weighed, and sampled for the yield determinations. The pulp was 
then screened again and made up into a sheet as described. 

Tho methods used for determining dry weights, yields, quality 
of pulps, and composition of liquors are given in the appendix. 

TEST MATERIALS USED. 
WOOD. 

The test material consisted of .'! 1 logs of aspen (Popvlus fr< muloides, 
Michx.) cut from representative trees growing intermixed with 
white birch near Rhinelander, Wis. Tho trees were of seed growth 
and had attained an average height of 44 feet, with straight, clear 
lengths of about 22 feel from which the logs were cut. 

The ages of the logs varied from 28 to 42 years, as determined by 
counting the annual rings. The logs were fairly free from knots, 
considering the size of the trees and the species. Volume-weight 
determinations on 36 samples, representative of the whole shipment, 
showed the average bone-dry weight per cubic foot of green or 



PRODUCING SODA PULP PROM ASPEN. 15 

unseasoned wood free from knots to be 26.68 pounds. The samples 
ranged from 23.6 to 31.4'pounds per cubic foot. 

As a rule the test material was sound, but some of the logs had 
decayed hearts. The material was peeled by means of a carpenter's 
drawknife; all decayed portions on the outside of the pieces and all 
protruding knots were chopped off. This cleaned wood was then 
sawed into disks five-eighths inch thick in the direction of the grain. 
Butts, tops, and all disks containing decay or other defects were 
culled. 

The remaining sound disks were split with the grain into chips 
1 inch to 6 inches by one-fourth inch by means of a special guillo- 
tine chipping machine. All knots were culled. The chips were 
then seasoned to constant air-dry weight, thoroughly mixed and 
screened to remove sawdust and dirt, and finally stored in cans to 
await the cooking tests. 

COOKING CHEMICALS AND SOLUTIONS. 

In ordinary mill practice the soda cooking liquors are made as 
described on page 4. The freshly causticized solution contains 
caustic soda (NaOII) for the most part, but a small amount of soda 
ash (sodium carbonate, Na 2 C0 3 ) still remains uncausticized. Various 
impurities are also present, but these are considered to have no 
effect in cooking. 

In the experiments the cooking solutions were made by dissolving 
fused caustic soda, 76 per cent l sodium oxide (Na 2 0), in water. 
The resulting solution was similar to the solutions used in commer- 
cial practice so far as caustic soda and soda ash are concerned, and 
there is no reason to believe that the results should be different in 
any way from those which would have been obtained by the use of 
commercial liquors of the same concentration and causticity. 

EFFECTS OF VARIATIONS IN THE COOKING CONDITIONS. 

The influence of the variable cooking condition in each group of 
tests on resultant yields and properties of pulps and consumption 
of cooking chemicals is shown graphically in figures 4 to 15. 2 The 
same results in greater detail are given in Tables 10 to 14 of the 
appendix. While, in general, the tests were carried out in accord- 
ance with the plan which has been described, minor departures could 
not be avoided, and the location of certain points on the diagrams 
are more or less affected by such variations. For this reason the 
tabulated data should be consulted for the exact conditions of each 
cook. 

1 Manufacturer's analysis. 

2 The numerals opposite each platted point on the curves are the serial numbers of the cooks. (See 
Tables 10 to 14.) 



16 BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 

YIELDS. 

The effects on yields of pulp and screenings are expressed by the 
curves in figure 4, in which the yields are plotted against the amount 
of caustic soda, the duration of cooking, the pressure of cooking, and 
the initial concentration of caustic soda. 

AMOUNT OF CAUSTIC SODA. 

With increases in the amount of caustic soda per pound of wood 
the yield of total crude pulp decreased at the rate of about 1 per 
cent for each 2 per cent of caustic (0.02 pound NaOH per pound of 



9 60 
111 


S 






























$■ 






1 




















!_ 50 






/ 


'* 


•r 












-' 








■XL 






' 
























o 




/ 




















4 






UI 
a. 































3 60 
































N 


v~ 


-j 




























i- 50 






/ 










ii ■ 














iS 




/ 


















10 












a. 


J 


1 































































.10 .20 .30 .40 

POUNDS NaOH PER POUND OF WOOD 



2 4 6 8 10 12 

DURATION AT MAX. PRESSURE-HOURS 



3 20 

UI 




\ 






















































>- 
t- 10 




9 






























\ 
























<-> 

a 

UJ 

a. 








v 




7 




« 




» 




4 












e 

























\ 
































_l CV 

UJ 


k 


I 






























>- 


































!?i 10 




\ 






























o 

<r 

at 






\ 


15 




4 


1 


1 


1 


2 


K> 
























' 


f 











.10 .20 .30 .40 

POUND NaOH PER POUND OF WOOD 



2 4 6 8 10 12 

DURATION AT MAX. PRESSURE-HOURS 



3 60 
ui 

t- 50 



40 

































22* 








20 
























II 1 








































IS 




"Tr 































































3 60 

UI 


































































£ 50 

UI 




26 








i 


j ' 






_24, 
























25 
















23 ' 








c 40 

UI 

a. 



































































60 70 80 90 100 110 120 
MAX. PRESSURE-PDS. PER SQ. IN. 



40 50 60 70 80 90 100 110 
CONCENTRATION NaOH-GRAMS PER LITER 



O -TOTAL CRUDE PULP 



• -SCMKHEDUMUACHED PULP 



Fig. 4.— Effects of cooking conditions on yields of total crude pulp, screened unbleached pulp, and 

screenings. 

wood). The yield at zero caustic soda would probably fall between 
80 and 90 per cent, being influenced only by the cooking effect * of 
the water condensed from the steam used in cooking. For high 
amounts of caustic soda the curve tends to approach parallelism 
with the horizontal axis. The yield would not be expected to become 
zero unless exceedingly large amounts of caustic were used. 2 

For amounts of caustic soda above what may be considered the 
minimum for successful cooking under the conditions used, the yield 

> See Tauss's experiments, 'Pablo l. 

s Tauss used for a single boiling as high as 7 pounds of caustic soda per pound of wood, and the yield 
or undissolved material after three hours at 58.8 pounds per square inch steam pressure amounted to 8.52 
per cent for beech and 2.87 per cent for pine. With 4 pounds caustic soda per pound of wood in each of 
three successive three-hour treatments under a steam pressure of 132.3 pounds per square inch, the yields 
for the two woods were 20.61 per cent and 18.20 per cent, respectively. This latter proportion of caustic 
soda was ten or mere times as great as is ordinarily employed in commercial practice. Aiso the other 
cooking conditions were proportionately more severe. 



Bui. 80, U. S. Dept. of Agriculture. 



Plate 




PRODUCING SODA PULP FROM ASPEN. 17 

of screened unbleached pulp was identical with that of crude pulp, 
but for smaller amounts of chemical it rapidly approached zero, 
while under the same conditions the screenings curve naturally 
approaches and becomes coincident with the curve for the total 
crude pulp. In this group of tests the minimum amount of caustic 
soda for successful cooking, so far as yields alone are concerned, is 
somewhere between 15 and 20 per cent. 

DURATION OF COOKING. 

The duration of cooking at maximum pressure influenced the 
yields in very much the same manner as did the amount of chemical. 
The yield of total crude pulp decreased about 1 per cent for each 
additional hour of cooking at maximum pressure. However, the 
curve (fig. 4) seems to approach parallelism with the horizontal axis, 
thus signifying that beyond a certain point cooking would have had 
no further effect. 1 The time allowed for these cooks to reach the 
maximum pressure was one hour, and the extended curve indicates 
a yield of about 60 per cent for zero hours duration at maximum 
pressure. This shows that the greater part of the cooking was 
accomplished during the first hour, or before the maximum pressure 
was attained, since during that hour about 40 per cent of the wood 
substance had been dissolved and the dissolving effect during the 
next 12 hours was only one-fourth as great. 

As determined by the yield curves, the minimum duration for 
successful cooking under the conditions employed was between one 
and three hours at maximum pressure. No tests were made between 
these two points. 

PRESSURE OF COOKING. 

The curve showing the influence of maximum cooking pressure or 
temperature on yields indicates that all of the tests were made at 
pressures above the minimum required for successful cooking, under 
the conditions employed for these tests; hence, no screenings were 
obtained from any of the cooks, and the curve for screened unbleached 
pulp coincides with that for total crude pulp. Increases of pressure 
from 70 to 120 pounds per square inch resulted in decreasing the 
yields of pulp about 1 per cent for each five pounds, which indicates 
that the higher pressures increase the thoroughness of cooking, other 
conditions being constant. 

CONCENTRATION OF CAUSTIC SODA. 

The tests varying the initial concentration of caustic soda in the 
digester liquors were also made within limits that resulted in thorough 
cooking for all of the tests. Increasing the concentration under the 

1 Figures 12 and 13 show that the active cooking chemical was consumed at the end of 7 hours a1 maxi- 
mum pressure: it is therefore not apparent from these tests what would be the elTcct of continued cooking 
in the' presence of available -caustic soda. 

31091°— Bull. -80— 14 2 



18 



BULLETIN 80, 1^. S. DEPARTMENT OF A.GBICULTUBE. 



conditions employed resulted in decreasing the yields of pulp about 
1 per cent for each 13 grams per liter increase in concentration. It 
is thus evident that with a given amount of chemical the greater 
cooking effect is secured by means of the more concentrated solutions. 
A practical limit of course exists at the point where the volume of 
the digester liquor becomes too small to afford favorable cooking 
conditions. 1 

PROPERTIES OF UNBLEACHED PULPS. 



NATURAL COLOR. 



150 



WO 



50 



»! 


















8 


*7~ 


- £.1 


i 


f | 










* 4 





.10 



.20 .30 .40 
POUNDS NaOH PER POUND OF WOOD 



100 



50 



100 



50 



"^ 



«a- 



JS&- 



2 4 6 8 10 12 
DURATION AT MAX. PRESSURE-HOURS 



_2£1L 



3 



60 



70 80 90 100 110 120 
MAX. PRESSURE- PDS. PER SQ. IN. 



Curves indicating the effects of the conditions of cooking on the 
natural eolor of the unbleached pulps are shown in figure 5. 

The larger the amount of 
caustic soda used per pound 
of wood the lighter in color 
was the pulp, as indicated by 
the "parts black" color rat- 
ing, but the curve approaches 
parallelism with the horizontal 
axis as the amounts of caustic 
increase. White pulps or those 
with zero "parts black" would 
not be obtained even if exceed- 
ingly large amounts of chemi- 
cal were used. 

Longer periods of cooking 
produced lighter-colored pulps 
up to the point where the 
maximum yield of screened 
pulp was obtained. Beyond 
this point there was a tendency 
for the pulp to become slightly 
darker as the duration of cook- 
ing was increased. This was probably due to the pulp fibers absorbing 
and retaining coloring matters from the "black liquors." It is gen- 
erally believed that as the cooking becomes more thorough the 
cellulose of the fibers gradually becomes more gelatinous or hydrated, 
and would therefore tend to retain coloring matter during the subse- 
quent leaching and washing treatments. 

The pressure (temperature) of cooking seems to have had compar- 
atively little effect on the color of the pulp within the range investi- 
gated. 

1 As the initial concentrations increased, the volumes of digester liquors at the start of cook decreased 
(see fig. 17), since the amount of caustic soda was held constant. Hence, increasing concentrations would 
eventually result in a volume of digester liquor so small that tho whole charge of chips would not be covered 
until late in the cooking period after the liquor had been sufficiently diluted by tho condensed steam used 
in cooking. In this case part of the chips would receive very severe treatment, while the remainder would 
more or less escape the cooking effect. The resulting pulp would represent .1 composite of the two con- 
ditions. 



100 



50 













zt 






2 


«' 




2«T 



40 50 60 70 80 90 100 110 
CONCENTRATION NaOH -GRAMS PER LITER 
Fig. 5.— Effects of cooking conditions on the color 
("parts black") of pulp. 



PRODUCING SODA PULP FROM ASPEN. 



19 



The more thorough cooking resulting from the higher initial con- 
centrations of caustic soda produced lighter-colored pulps, although 
the lower limit of Che cooking condition in these tests was considerably 
above the minimum for successful cooking. 

While the several curves shown in figure 5 indicate for each group 

of tests more or less change in the "parts black" color ratings or the 

depth of color, the hues of the 

1000 



pulps were 
affected. 



not materially 



OCCURRENCE OF SHIVES. 

Shives are most numerous 
in pulps from the less severe 
cooks and are entirely absent 
from those thoroughly cooked. 
The shives curves (fig. 6) bear 
some resemblance to those for 
the yields of screenings, but 
shives disappear from the pulps 
only under somewhat more 
severe cooking conditions than 
those which reduced the yield 
of screenings to zero. At the 
point of maximum yield of 
screened pulp the cooking has 
progressed far enough for the 
fibers to become more or less 
separated from each other, but 
not completely so, since some 
of them still remain in groups 
(shives) small enough to pass 
the screen slots. But as the 
cooking becomes more severe 
the fibers are entirely sepa- 
rated, and the resulting pulp 
is free from shives. In gen- 
eral, increasing the amount of 
temperature of cooking, or the 
liquor decreases the "shiviness" 



800 
600 
400 
.200 



800 



600 



400 



200 



1 


\ 














\ 














\\ 


'e 












\ 
















V 


< 


ft — 1 


£— Si 





.20 .30 .40 
POUNDS NaOH PER POUND OF WOOD 



"\ 
















— N 


V 
















\ 


















V 


13 

1 


12 

n 


10 







60 



2 4 6 8 10 12 
DURATION AT MAX. PRESSURE-HOURS 



70 80 80 100 110 120 
•MAX. PRESSURE- PDS. PER SQ.IN. 



26 1 






25 


24 


l 


— 2, 


1 



200 



'40 SO 60 70 80 90 100 110 
CONCENTRATION NaOH-GRAMS PER LITER 

Fig. 6. — Effects of cooking conditions on the occur- 
rence of shives in pulp. 

caustic soda, the duration or the 
initial concentration of the digester 
of the pulp. 



ASH CONTENT. 



The curves in figure 7 indicate that increasing the thoroughness 
of cooking within certain limits decreases the ash content of the pulp*; 
outside of these limits the ash content may be increased. 

Since the normal amount of ash in aspen wood is not over three- 
quarters of 1 per cent, the high amounts in the pulps produced 



20 



BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 



from this wood in some of the tests is probably due to the presence 
of cooking chemicals ' which were not completely removed during the 
washing treatments. Increasing amounts of ash as the cooking 
conditions become more severe may be duo to a difference in the 
physical character of the cellulose produced under such conditions 
and the resultant increased difficulty of leaching out and washing 
away any residual and absorbed mineral matters. No tests were 

made to determine the char- 
acter of the ash from any of the 



20 



1.5 



Q. 1.0 



0.5 



1 

< 


19 

L 
















V 
















* 


r-V 


6, 


5j 


^^"4 













pulps. 



STRENGTH. 



.10 



.20 .30 .40 
POUNDS HaCH PER POUND OF WOOD 



Z.C 



1.0 



L0 



0.5 



1.0 













"• 






^6 






13 












^"-tt- 


14 




• 
12 









2 4 6 8 10 12 
DURATION AT MAX. PRESSURE- HOURS 



0.5 



it 


21' 


1 T~ ^ 


» 1 i 






m] i? 







60 



70 80 90 100 110 
MAX. PRESSURE PDS. PER 



120 

•CLIN. 



The strength of a pulp de- 
pends chiefly upon three fac- 
tors — (1) the strength of the 
individual fibers ; (2) the felting 
or matting quality of the fibers ; 
and (3) the presence of gelatin- 
ized fibers and other matters 
which act as cementing ma- 
terials. 

Severity of cooking is at- 
tended by a weakening of the 
cell walls and may result in a 
decrease in the strength of the 
pulp. This decrease of strength 
was strongly marked in the tests 
in which the more severe cook- 
ing conditions were produced 
by increasing the amount of 
caustic soda. It was most rapid 
up to the point where the fibers 
were completely separated (indicated by the absence of shives), be- 
yond which it was less pronounced. For increasing durations of 
cooking the general trend 2 of the effect was the same as for 
increasing amounts of chemical, but the total decrease in strength 
was not quite so great in amount for the range of cooking conditions 
investigated. 

1 Special precautions were taken to eliminate the influence of dirt. Further it does not seem reason- 
able that the cooking action which removed the lignin and other organic matters should have produced in 
the fibrous residue or pulp a concent rat ion of t he mineral const ituents which go to form the wood ash. 

2 The data are no 1 sufficient for expressing the effect In detail. The true curve wi mid be expected to 
have a hend coinciding with the point of maximum yield of screened pulp or the poinl where the shives 
are reduced to zero. 



1.0 



0.5 



36* 




25 




*♦, 




I - 










1 



40 



50 60 70 80 90 100 110 
CONCENTRATION NaOH -GRAMS PER LITER 



Fig. 7.— Effects of cooking conditions on the ash 
content of pulp. 



PRODUCING SODA PULP FROM ASPEN. 



21 



Increasing the pressure and increasing the initial concentration 
bevond a certain point both increased the strength of the pulp. 
This effect is apparently contradictory to that found for the other 
two groups of tests and may possibly be due to the high tempera- 
tures and high concentrations which would tend to cause a physical 
change in the cellulose with in- 
crease of the cementing effect 
mentioned previously. 

Curves showing the influence 
of cooking conditions on the 
strength of pulp are given in 



3.5 



- 3.0 



2.5 



w 2.0 



figure 8. 



EASE OP BLEACHING. 

The chief purposes of bleach- 
ing are (1) to produce a white 
pulp and (2) to destroy any non- 
cellulose materials which tend 
to make the pulp less durable. 
The more nearly the original 
pulp approaches to pure cellu- 
lose the less is bleaching re- 
quired. However, difficulty of 
bleaching is occasioned not only 
by the presence of ligneous mat- 
ters, but also by coloring mat- 
ters absorbed in the cell walls 
from the "black liquors" and 
by the residual cooking chem- 
icals which the leaching and 
washing treatments have failed 
to remove. In the latter case 
a certain amount of bleach is 
neutralized by reactions with 
the other chemicals. 

Curves expressing the effects 
of varying the cooking condi- 



1.5 



■■ \ .. 














\ 


















7*~-~. 




>e 


s 
















"^S" 







i0 .20 .30 .40 

POUNDS HaOH PER POUND OF WOOD 



3.5 



30 



g 2.5 



2.0 



3.5 



§ 3.0 



£ 2-5 



















(6"~~ 




14 


-~i2L 


w 










• 
IS 








10*" 







2 4 6 8 10 12 
DURATION AT MAX. PRESSURE-HOURS 



a. 2.0 











i 


^ 


'17 






22 






19 










\2! 




20 











60 



70 80 SO 100 110 120 
MAX. PRESSURE-PDS. PER SQ. IN. 



3.5 



8 3.0 



* 2.5 



°- 2.0 















J 


L 












s 


/ 










23 




24 






26 







40 



50 60 70 80 90 100 110 
CONCENTRATION NaOH -GRAMS PER LITER 



Fig. 8. — Effects of cooking conditions on the strength 
of pulp. 



tions on the ease of bleaching, as measured by the amount of bleach 
required to bring the pulps to a standard white color, are shown in 
figure 9. These curves show that under the conditions of cooking the 
residual ligneous matters are the most important factor in determin- 
ing the amount of bleach required, since the more thorough cooking pro- 
duces pulps that are more easily bleached. The decrease in amount of 



22 



BULLETIN SO, LI. S. DKl'AUTMKNT OF ACUilOULTURE. 



bleach required was very rapid up to the point where shives were 
eliminated; beyond this point the effect was less marked. It must 
not be assumed, however, that the shives alone necessitated the larger 
amounts of bleach. The presence of shives indicates an incomplete 
cooking reaction and implies that considerable ligneous matter may 
remain in the other (completely separated) fibers. 

The effect of severity of the 
cooking conditions is especially 
noticeable in the curves for the 
tests varying the amount of 
caustic soda and the duration 
of cooking, since certain of the 
pulps produced in these tests 
were less thoroughly cooked 
than any of those from the 
other groups. 



30 



20 



10 



> I I T" 



.20 .30 .40 
POUNDS NaOH PER POUND OF WOOD 



30 



* 20 



V s 


















S>I5 


--t! 


IS 


12 

— • 


















— •— 
10 







LOSS ON BLEACHINO. 



2 4 6 8 10 12 

DURATION AT MAX. PRESSURE-HOURS 





(2 2 


21 


20 


















19 * 


1 * 







70 80 90 100 110 120 
MAX. PRESSURE-POS. PER SQ. IN. 



The curves showing the 
losses on bleaching as affected 
by the varying cooking condi- 
tions are given in figure 10. 
As would be expected, the loss 
decreased with thoroughness 
of cooking. In the tests vary- 
ing the amounts of chemical 
and the durations of cooking 
the rate of decrease in bleach- 
ing loss with greater severity 
of cooking was fairly constant, 
but it is probable that if the 
cooking conditions were ex- 
tended for higher values than 
those used the curves would 
approach parallelism with the horizontal axis. Such an effect was 
obtained for the tests in which the cooking pressures were varied. 
It is not reasonable to believe that more severe cooking would result 
in pulps which would sufier no loss whatever on bleaching. 

The platted points for the tests hi which the initial concentrations 
were varied are so few in number and so irregular in location that 
they give little indication of the influence of this factor. How T ever, 
additional information is obtained from some earlier tests of the Forest 
Service, summarized in Table 4. 



20 



o 

eo 



eo 



o 

40 





2« 




















•"S 




24 


' 


>zT 



Fig. 9. 



50 60 70 80 90 100 HO 
CONCENTRATION HaOH-GRAMS PER LITER 
Effects of cooking conditions on the ease of 
bleaching. 



PRODUCING SODA PULP PROM ASPEN. 23 

Table 4. — Effect of concentration on bleaching losses (autoclave tests). 1 



Cook 
No. 


'Concentra- 
tion of 
NaOH. 


Yield of 

total crude 

pulp. 


Yield of 
screenings. 


Bleach 
required. 


Loss on 
bleaching. 


1 
2 

4 


Grams per 
liter. 
80 
50 
30 


Per cent. 
41.10 
44.23 
46.97 


Per cent. 

0.10 

.03 

.07 


Per cent. 
15.4 
14.7 
15.8 


Per cent. 
3.92 
4.08 
4.68 






a* 


r-C. 




.< 5 
















4« 







.20 .30 .40 

POUNDS NaOH PER POUND OF WOOD 



CD 2 



1 Each cook employed seven hours' duration at 110 pounds pressure per square inch. The caustic soda 
charged amounted to 0.25 pound per pound of wood. For complete information see appendix, Table 15. 

These data indicate that increasing the concentration reduces the 
loss en bleaching, hence the curve in figure 10 has been drawn to show 
such an effect. This is sub- 
stantiated by the fact that 
varying the amount of chemi- 
cal and the duration and pres- 
sure of cooking in each case 
showed a reduction in the 
bleaching losses as the severity 
of cooking increased, and that 
most of the other curves for 
the effect of concentration 
(especially the yield, shives, 
and bleach-required curves) 
show more severe cooking with 
the higher concentrations. 

The relatively large amount 
of loss in the case of cook 23 
does not seem to be warranted 
in view of the well-cooked con- 
dition of the pulp. However, 
the comparatively high strength 
of the pulp indicates an abnor- 
mal condition. 

The loss in weight of a pulp 
during bleaching is due prima- 
rily to the removal of the col- 
ored ligneous matters and to 
the partial destruction of the 
cellulose itself. The latter is fig.io. 
especially liable to occur if the 
bleaching treatments are severe, or if the cooking treatments have left 
the cellulose in an easily oxidized condition, so that it is either dis- 



V 
















\ 


\l 5 
















\ 


s 


13 

• 














•N 




















^12 


to 







2 4 6 8 10 12 
DURATION AT MAX. PRESSURE-HOURS 



\ 


\ 
















s 

21 


i— 


1 


>" , 


l" . 


n 




( 


>*o 











60 



70 80 90 1G0 110 120 
MAX.PRESSURE-PDS.PER SQ.IN. 







« 


r" 






* 


*1 


— —i 

26 


p 1 






< 


24 







40 



50 60 70 80 90 100 IK) 
CONCENTRATION NaOH -GRAMS PER LITER 

-Effects of cooking conditions on the bleach- 
ing loss. 



24 



BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 



solved during bleaching or broken up into small particles, which are 
removed in the washing operations. The partial removal of the min- 
er.;! or ash-forming constituents from the pulp may also occasion some, 
loss. On the other hand, the ash in bleached pulp sometimes tends 
to increase over thai for the unbleached pulp (due to an accumulation 
of lime compounds and other residues from the bleaching solution), 
and hence may offset the loss due to other causes. 

RELATION BETWEEN PROPERTIES AN!) YIELDS. 

Many of the curves expressing the effects of the varying cooking 
conditions on the properties of the unbleached pulps have bends or 

30 































1 




TKST VARYfNG 

o AMOUNT OF CAUSTiC SODA 
ODURAT'.ON OF COOKING 
« PRESSURE OF COOKING 
©CONCENTRATION OF CAUSTIC SODA 
©PRELIMINARY TEST 














































I 




































































































o 
























































JLS- 


^ • 




















a 


a 




• 














e 








• 


< 


» 

















































44 46 48 SO 52 54 56 58 

YIELD-TOTAL CRUDE PULP -PER CENT 

Fig. 11. — Relation between yields and ease of bleaching. 

"breaks" at or near the values for the cooking conditions which 
resulted in the highest yields of screened pulp. So general is this 
that, with decreasing severity of cooking, the occurrence of sudden 
changes of direction for curves expressing properties affords a reliable 
indication that the yield of screened unbleached pulp is near its maxi- 
mum. This is especially evident in the curves for ease of bleaching. 
That properties of pulps are directly dependent upon yields is well 
illustrated when amounts of bleach required are platted against yields 
of total crude pulp, as in figure 11. Values for all of the cooks made- 
in these experiments have been platted, irrespective of the testing 



PRODUCING SODA PULP FROM ASPEN. 25 

conditions under which they were secured. It is evident that cooks 
which resulted in decreased yields produced easier bleaching pulps. 
For the higher values slight differences in yields are accompanied by 
marked differences in the ease of bleaching, but the effect rapidly 
diminishes until a large decrease in the yields affords little difference 
in the amounts of bleach required. This would be expected in view 
of the nature of the cooking reactions. The effect is first to remove 
the intercellular substances and part of the ligneous matters from the 
wood, then the cellulose itself begins to be attacked, and finally, after 
the greater part of ligneous matters has been removed, the cellulose 
alone is affected. The ease of bleaching is a measure of the amount 
of noncellulose matters present in the pulp. 

Other properties of the pulps when similarly platted against yields 
show more or less definite relationships, but are apt to be modified 
according to the cooking condition varied. For instance, when vary- 
ing the amount of caustic soda or the duration of cooking, decreased 
yields were attended by decreased strength of pulp; when initial con- 
centrations or pressures were varied, the strength increased as the 
yields decreased. Natural color, shives, and screenings, however, 
were little affected for yields below 54 per cent, no matter how pro- 
duced; for higher yields the color, shives, and screenings increased 
rapidly with increasing yields. The losses on bleaching followed 
fairly closely the amounts of bleach required, and hence decreased as 
the yields decreased. 

SIGNIFICANCE OF PROPERTIES. 

There are at present no accepted standards of quality or market 
grades of soda pulps. What may be sufficiently good quality for one 
purpose or one mill may be poor or medium quality for another. 
Aside from bulkiness and opacity, which depend mainly on condi- 
tions not studied in these experiments, the desirable properties of a 
pulp are, in general, as follows: 

(1) Low percentage of bleach required. 

(2) Low loss on bleaching. 

(3) High strength. 

(4) Durability (resistance to wear and decomposition). 

(5) Low ash content. 

(6) Few shives. 

(7) Absence of dirt. 

(8) Light color for the unbleached pulp. 

(9) Whiteness of the bleached pulp with freedom from certain undesirable tints. 

It is not often that any one pulp has the advantage over another in 
all of these properties, and for many uses some of them are of no 
importance. For aspen (poplar) or other short-fibered pulps used in 
the manufacture of book papers the properties which are given most 



26 



BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 



consideration are freedom from dirt and shives and low percentage of 
bleach required, with the attendant low loss on bleaching. Both 
undercooked and overcooked pulps are to be avoided. 



100 r^r 



90 



80 



70 
.10 



? 


















1 


1 ^^ 


1 


le 

























.20 .30 ,40 

POUNDS NaOH PER POUND OF WOOD 









^" 


12 


• 
10 








/W 9 


**** 












*/ 

















2 4 

DURATION 



6 8 10 12 
AT MAX. PRESSURE-HOURS 



CONSUMPTION OF CAUSTIC SODA. 

By consumption of canst ic soda is meant the neutralization of the 
free or active caustic soda (NaOH) existing as such in the digesting 

liquors. The neutralization re- 
sults from the combination of 
the sodium (Na) of the alkali 
with the acid products derived 
from the hydrolysis of the 
lignined fibers during cooking. 1 
The black liquors at the end 
of the cooking treatments con- 
tain in dissolved form these 
n on alkaline, sodium com- 
pounds, together with the re- 
maining free caustic soda. 

The effects of varying the 
cooking conditions on the con- 
sumption of caustic soda, ex- 
pressed in per cent of the 
amount charged or the effi- 
ciency in its use, are shown in 
figure 12. The actual con- 
sumption in pounds per 100 
pounds of wood is shown in 
figure 13. 

As would naturally be ex- 
pected, the greatest compara- 
tive efficiency for the cooks 
made with varying quantities 
of caustic soda resulted from 
the use of the smaller amounts. 
However, when very small 
amounts were employed, the 
cooking reactions were not sufficiently complete, 2 as indicated by the 
curves for yields and properties of the pulps. In this group of tests 
well-cooked pulps were first obtained with about 0.2 pound of NaOH 
per pound of wood. The efficiency in the use of the caustic at this 
point was about Sf> per cent. 

1 See De Cew's discussion, p. G. 

2 It is a well-known chemical law thai in order to carry a reaction to a given degree of completion for one 
of the reacting substances it Isnecessary to haveavaUableaoertamexce&softheotharchemical.or chemicals 

which take part In the reaction. 'Phis means that the efficiency In the use of the chemical can not be 100 
per cent. The speed of the reaction is proportional to the amount of the excess. 



100 



90 



60 



70 



100 



90 



60 



^ 70 











( 


£ , 


17 










s'i 


,'9 








i 


w A 


,21 


> 20 











60 



70 80 90 100 IK) 120 
MAX. PRESSURE- PDS. PER SO.. IN. 



100 



90 



80 





26 


















< 


55 — 




24 


< 


23 

1 



40 



SO 60 70 80 90 100 110 
CONCENTRATION NaOH -GRAMS PER LITER 



12. — Effects of cooking conditions on the effi- 
ciency in the use of caustic soda. 



PRODUCING SODA PULP FROM ASPEN. 



27 



40 



30 



20 



























6 


's 








£--1 


r'* 7 













.10 



.20 .30 40 

POUNDS NaOH PER POUND OF WOOD 





15 


14 


•" 


t" 


10 














-"*» 

















2 4 6 8 10 T2 
DURATION AT MAX. PRESSURE-HOURS 



With increasing durations of cooking the efficiency in the use of 
caustic soda increased until it reached a constant maximum value. 
An efficiency of 95 per cent was obtained by seven hours' cooking at 
maximum pressure, and, since no greater efficiency was secured by 
continuing the cooking four additional hours, it is apparent that this 
represents the maximum efficiency attainable. That the cooking 
reactions are not due entirely to the presence of active caustic soda 
is indicated by the fact that after the 95 per cent efficiency had been 
attained increased durations resulted in some further cooking effect 1 
(see curves for yields and prop- 
erties of pulps) with no increase 
in the amount of chemical con- 
sumed. Increasing the pres- 
sure also resulted in greater 
efficiency in the use of caustic 
soda until a maximum of 95 
per cent was obtained. 

In all groups of tests in which 
a constant amount of caustic 
soda was charged into the di- 
gester for each cook, greater 
percentage efficiency in its use 
could mean only a greater 
actual consumption of the 
chemical. In the group of 
tests varying the amounts of 
caustic soda, the decrease in 
percentage efficiency was ac- 
companied also by increase in 
the actual consumption. It is 
thus apparent that the more 
thorough cooking, whether 
produced by increasing the 
amount of chemical in the 
charge or the duration or the 
pressure of cooking, is, in large part at least, due to the greater com- 
pleteness of the reaction between the chemical and the wood. 

The tests employing various initial concentrations of caustic soda 
in the digester liquors (the amount of caustic soda charged remaining 
the same) seemingly do not bear out this conclusion. In most 
respects the determinations of yields and properties of the pulps in 
these tests indicated that the more concentrated solutions resulted 
in more thorough cooking, but no increase in the consumption of 
chemical occurred; in fact, with increase of concentration, a decrease 



30 



20 



30 



20 











iT5 


M 


TT 




2* 


21 




20 











60 



70 80 90 WO 110 120 
MAX. PRESSURE-PDS. PER SQ. IN. 




50 GO 70 80 90 100 IK) 
CONCENTRATION NaOH -"GRAMS PER LITER 

Fig. 13.— Effects of cooking conditions on the amount 
of caustic soda consumed. 



1 For the effect of water alone, see Tauss's experiments, Table 1 . 



28 



BULLETIN 



U. S. DEPARTMENT OF AGRICULTURE. 



of consumption and subsequently decrease of percentage efficiency 
are indicated. While the possibility of error is not eliminated, 1 this 
result indicates the need for further investigation. 



RELATION BETWEEN CAUSTIC SODA ( '< >NS I'M KI) AND YIELDS. 

For the purpose of further studying the cooking effects of the 
various conditions employed, yields of total crude pulps from all of 
the cooks were platted against amounts of caustic soda consumed 
per 100 pounds of wood charged (fig. 14). The average curve drawn 
through these points indicates a definite relation between yields and 



84 

80 

£ 76 
o 

S 72 

(L 
1 

5 68 

Q. 

S 64 

2 
o 

_i GO 

fss 

o 
£ 52 

48 

44 




































TEST VARYING 

»C0HCENTRATI0N OF CAUSTIC S00A 
©AMOUNT OF CAUSTIC SODA 
ODURATI0N OF COOKING 
©PRESSURE OF COOKING 
©PRELIMINARY TEST 






































































o > 




€> 
























6 ^j 


o 


o 


< 


> 




















( 


i 


i. 

• 




s-_o 
























o 






o 







10 12 14 16 18 20 22 24 26 28 30 32 
NaOH CONSUMED PER 100 PDS.0F BONE DRY W00D-PDS. 



34 



Fig. 11. Relal ion bel ween yields and amount of caustic soda consumed. 

amounts of caustic soda consumed, regardless of the cooking condi- 
tions. However, even if it is assumed that the location of some of the 
points is duo to experimental errors, the 1 relation, as regards individual 
cooks, can be only an approximate one, since it has already been 
pointed out that in some of the tests increased cooking effects were 
obtained without any increase in the consumption of caustic soda. 
If the curve were produced for lower amounts of caustic soda, the 
yields would probably be somewhere between 80 and 100 per cent 
at zero consumption, since under these conditions cooking could still 
be effected by water alone. 2 

i The test data show a loss of digester liquor overflowing through the "top relief" for cooks 25 and 26 
(that for cook 26 showing the greatest loss), and it is due to the platted points for these two cooks that the 
curves indicate greater consumption of caustic soda at the lower concentrations. 

- See Tauss's experiments, table 1. 



PRODUCING SODA PULP FROM ASPEN. 29 

Since the completion of these experiments Mr. E. Sutermeister has 
published * the results of some tests in which a small rotary autoclave 
and copper flasks were used as cooking vessels. Yields varying from 
93 to 24 per cent and consumptions of caustic soda varying from 
to 29 pounds per 100 pounds of wood were obtained, 2 giving a relation 
similar to that indicated by the curve in figure 14. However, in his 
experiments a greater reduction of yields was obtained per unit 
decrease in the caustic soda consumed, which is probably due to 
differences in test material, method of experimentation, and appa- 
ratus employed. 

The actual consumption of caustic soda during cooking is a factor 
which is not given sufficient consideration in commercial practice, 
although it is one of considerable importance for an intelligent control 
of the cooking operations. By a careful study of the consumption, 
together with the other effects of the various cooking conditions, it is 
possible to determine the best operating conditions. That pulp 
mills do not ordinarily determine the consumption of caustic soda and 
the efficiency of its use is due to the length of time necessary for the 
analysis of the black liquors. While the method used in these experi- 
ments requires some time for carrying out the analysis, its occasional 
use in commercial operations would be of benefit in determining the 
conditions to be used in future cooks. 3 If there were a rapid and 
accurate method of analysis such as is used in sulphite mill operations, 
it would assist in determining when the cooking had progressed far 
enough, at which time the digester could be blown. Production of 
undercooked or overcooked pulps would thus be avoided. 

SEVERITY OF COOKING AS INDICATED BY MICROSCOPIC APPEARANCE OF FIBERS. 

A good indication of the thoroughness or severity of cooking may 
be obtained by microscopic examinations of the pulp fibers. 4 The 
effects of varying the cooking conditions are shown in figure 15; 
curve A represents the relative abundance of vessels in the pulps; 
curve B, the ray cells; curve C, the fiber bundles or shives; curve D, 
the prominence of the vessel markings; and curve E, the apparent 
strength of fiber walls. Since there are no absolute units for measur- 
ing these effects, the ordinates as shown for each curve represent 
arbitrary units ranging from to 10. The photomicrographs in 
Plates II to VII, inclusive, present some of the more pronounced 

' Paper, p. 15, No. 2, vol. 9, Sept. 25, 1912. 

2 In obtaining yields higher than 75 per cent the test material was treated at atmospheric pressure. Under 
this condition the cooking effect of water alone would have but little influence unless long durations of 
treatment were used. 

3 The boiling of rags with caustic-soda solutions for the production of rag pulps Is controlled in this manner. 
* For the normal appearance of libers in 1 he uncooked w ood see i'lates VIII and IX , as well as the discus- 
sion on p. 42. 



30 



BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 



effects. 1 While various gradations resulted, 2 the experimental pulps 
may be classified in the following three groups: 

Overcooked pulps.— Severe digestion treatments resulted in "over- 
cooked" pulps, examples of which are seen in Plates II and III. 
The walls of the fibers show a considerable degree of weakness, 
as indicated by their thin transparent appearance and by their 
much twisted and fractured condition. The relative number of 
vessels present in the pulp is low as compared with the normal 
number present in the wood, and the pits and other markings on 
them are only dimly visible. Many of the vessels remaining are 



COOK NO. 


f ' \ 


17 


« S 4 


A 
















B 


1 


^N 


^ 
















» \ 


1 


C 




N 


^ 










D 


















1 


r^ — , 












E 

















COOK MO. 2i tl 



— i 

A 


i 1 


i 1 


• ( 


I 1 


> — _, 




















\ 


C ' 


^J 


1 1 


1 i 






>— « 


1 


D 














E 

















.10 .20 .30 .40 
POUNDS NaOH PER POUND OF WOOD 



60 



70 80 90 100 IK) 120 
MAX. PRESSURE- PDS. PER SO. IN. 




A 














-< 


» 


B 










1 ' 


i 






C 


















D 


— i 


i 1 






























E 


— < 


i 


< 


» 











2 4 6 8 10 12 
DURATION AT MAX. PRESSURE-HOURS 



40 50 60 70 80 90 100 110 
CONCENTRATION NaOH -GRAMS PER LITER 



Fig. 15.— Effects of cooking conditions on pulp fibers. A, abundance of wood vessels; B, ray cells; 
C, fiber bundles, or strives; D, prominence of vessel markings; and E, apparent strength of fiber 
walls. 

ragged and partly disintegrated; and the pulp, for the most part, 
is also characterized by an absence of the comparatively thin-walled, 
delicate ray cells. Fiber bundles also are absent, since these are 
made up of fibers bound together by groups of the brick-shaped ray 
or parenchyma cell. The indistinctness of the vessels and fibers is 
due chiefly to the removal of the ligneous infiltrations of the cell 
walls, in consequence of which the elements developed very little 
color from the particular stain used in making the microscopic 
mounts. 

Well-cooked pulps. — Pulps produced under less severe conditions 
are made up of stronger fibers, such as shown in Plates IV and V. 

1 The remarks following the title of each plate and the discussion in the text are not based on the fields 
shown in the photomicrographs alone. 

2 The photomicrographs, in the order of their sequence, show gradations of severity of cooking. 



PRODUCING SODA PULP FROM ASPEN. 31 

The milder treatments are apparent in the increasing number of 
ray cells and vessels, the latter being well preserved and showing 
their markings quite clearly. The fibers are twisted or broken to only 
a small extent, and yet are so well separated that there are no fiber 
bundles. 

Undercooked pulps. — Plates VI aDd VII illustrate the character- 
istics of undercooked pulps, and show plainly the mildness of the 
digestion treatments employed in their production. Well-preserved 
vessels with sharply defined markings are clearly visible, ray cells 
are numerous, and the walls of the fibers are less dissolved away 
than in the more thoroughly cooked pulps. Coincident with these 
characteristics there are also present many fiber bundles or shives* 
noticeable even when the microscopic slides are examined with the 
naked eye. Undercooked fibers develop a deep color from the particu- 
lar stain used in mounting, and on this account appear very distinct. 

Of the several groups of tests, the one varying the amounts of 
caustic soda per pound of wood resulted in the greatest range of 
severity of cooking as determined by the microscopic appearance 
of the pulp fibers. A small amount of chemical resulted in an under- 
cooked pulp. With increases in the amount the strength of cell 
walls gradually decreased, the wood vessels suffered gradual destruc- 
tion, and their markings were dimmed. The ray cells and fiber 
bundles disappeared soon after the point was reached where the 
maximum yield was attained. The higher amounts of caustic gave 
the overcooked effects. 

For varying durations of cooking the effect was practically the 
same, and undercooked pulps were obtained at the shortest duration 
used. However, the highest durations employed did not give as 
severely cooked pulps as were obtained with large amounts of chem- 
ical. While all of the tests varying the cooking pressures resulted in 
fairly well cooked pulps, there was a tendency toward undercooking 
at the lowest pressure used. The tests varying the initial concentra- 
tions also resulted in well-cooked pulps, except for the highest con- 
centration, where a slight overcooking effect was observed. 

INFLUENCE OF COOKING CONDITIONS ON COST. 

While it is not feasible from the data at hand to discuss all cost 
factors affecting the commercial production of pulps, the more direct 
effects of the cooking conditions employed can be shown. The actual 
effects on the cost of production, of course, depend upon various 
other operating conditions at any particular mill, but the general 
trend of the effects is the same, irrespective of local conditions. 

TIME. 

Shorter durations of cooking result in more efficient use of the 
digesting apparatus; more cooks can be made per day or per week. 



32 



BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 



and, as has been shown, yields of pulp per unit of wood are also 
increased, and consequently more pulp is secured per cook. The 
greater plant capacity thus obtained would result in a proportionate 
decrease of operating costs per ton of pulp. 

Figure 16 shows the production of pulp per 24 hours continuous 
operation for each 100 pounds of wood capacity of digester as influ- 
enced by various durations of cooking. The curve was derived from 
the experimental data, assuming a one-hour period for blowing the 
digester after completing a cook and for charging the next cook, and 

a similar period for 
attaining maximum 
cooking pressure. 
Thus, for a three-hour 
period at maximum 
pressure, the total 
time between the 
charging of two con- 
secutive cooks is five 
hours. Computation 
shows that decreas- 
ing the duration at 
maximum pressure 
from eight to five 
hours increases the 
daily output 48 per 
cent, while a decrease 
from ten to three 
hours increases the 
output 156 per cent. If the time allowed for blowing and charging 
the digesters and for raising the digester pressure is decreased, the 
increase in the daily output will be even more pronounced as the 
duration of cooking is shortened. 







































































































250 


































































































2 


















































§ 


















































£ 


















































i 200 


































































































a 


































































































th 


















































i 150 




















































































































































































































































| 100 






















































































































































































































































<M 



















































5 6 7 B 9 10 It 
DURATION AT MAX. PRESSURE-HOURS 



12 13 



Kig. 10. — Effect of duration of cooking on production in 24 hours. 



STEAM CONSUMPTION. 

While the consumption of steam varies with the duration of cook- 
ing, it is influenced also by the pressure maintained in the digester 
and more by the relative volumes of the liquor charge. Under the 
testing conditions employed, the volume of liquor varied both with the 
amount of caustic soda charged (the concentration being constant) 
and with the concentration (the amount of chemical being constant) . 
Since the heating was accomplished by steam blown directly into the 
digester, a measure of the amount of steam used is afforded by the 
increase in the volume of liquor during cooking. 1 The effects of the 

1 The steam used was not perfectly dry, containing a small amount of moisture or "priming." How- 
ever, as the steam was of approximately the same moisture content for all tests, the "condensation" was 
proportional to the amount of steam used. 



Bui. 80, U. S. Dept. of Agriculture. 



Plate II. 




Fibers of an Over-Cooked Pulp Produced with a Large Amount of Caustic 
Soda, i Cook 4.) Magnified 65 Diameters. 

Partial disintegration has taken place. The fibers are fragmentary and contorted with rather 
weak cell walls. The vessels with barely visible markings are on the point oi being 
eliminated. 



Bui. 80, U. S. Dept. of Agriculture. 



Plate III. 







Fibers of an Over-Cooked Pulp Produced with a High Concentration of Caustic 

Soda. (Cook 23.) Magnified 65 Diameters. 

The fibers are somewhat fragmentary. 



Bui. BO, U. S. Dept. of Agriculture. 



Plate IV. 




Fibers of a Well-Cooked Pulp Produced with a Medium Amount of Caustic 

Soda. (Cook 7.) Magnified 65 Diameters. 

This is a pulp of average good quality. Vessels are well defined. 



Bui. 80, U. 5. Dept. of Agriculture. 



Plate V. 




Fibers of a Well-Cooked Pulp Produced with a High Pressure of Cooking. 
(Cook 17.) Magnified 65 Diameters. 

Tli is is a strong, well-separated pulp. 



Bui. 80, U. S. Dept. of Agriculture. 



Plate VI. 



^%* 




Fibers of an Under-Cooked Pulp Produced with a Short Duration of Cooking. 

(Cook 16.) Magnified 65 Diameters. 
Many shives, consisting of two or more unseparated fibers which parallel each other, are present. 



Bui. 80, U. S. Dept. of Agriculture. 



Plate VII. 




Fibers of an Under-Cooked Pulp Produced with a Small Amount of Caustic 
Soda. (Cook 9.) Magnified 65 Diameters. 

Note the vessels with well-defined markingsand the ray cells holding together a group of fibers 

constituting a shive. 



PRODUCING SODA PULP FROM ASPEN, 



33 



cooking conditions on the resultant condensations are shown in figure 
17. Curves showing the initial volumes of digester liquors for two 
of the groups of tests are also included in the same figure. 

In the tests employing various proportions of caustic soda, the 
amount of liquor at the start of cook varied directly with the amount 
of chemical, as shown by the straight-line curve. The condensation 
also increased rapidly as the amounts were increased. The down- 
ward turn in the heavy-line curve for the higher proportions of caustic 
is caused by the digester becoming filled and overflowing through the 
top relief during the final stages of cooking. However, the dotted 



So 

_i 

u.o .4 



9 



.10 .20 .30 .40 

POUNDS NaOH PER POUND OF WOOD 



o£ 40 



— 2i< 


\ 


^ 






l| 1 












,24 




£3 



50 60 70 80 90 100 110 
CONCENTRATION NaOH -GRAMS PER LITER 



14 
5 12 

e i.o 

























f y 










£, 


8, 


2&"^ 






4* 





.10 .20 .30 .40 
POUNDS NaOH PER POUND OF WOOD 



5E 
« 1.4 

£1.2 



K 





























». 




2 V 










26 , 






r 15 











1.0 
40 50 60 70 80 90 100 110 

CONCENTRATION NaOH -GRAMS PER LITER 



z 12 
§1.0 









13 
• > 


•'5 


~ar 


















It 




r^» 


# .4 











C 2 4 6 8 10 12 
DURATION AT MAX. PRESSURE"" HOURS 



a 1 - 2 

81.0 



















22 


2 *1 


» *$ 


1 '* 


18, 




fj 




— ■< 


1 H 




' ( 


> 



















60 70 80 90 100 110 120 
MAX. PRESSURE -PDS.PEJJ SO. IN. 



Fig. 17. — Effects of cooking conditions on initial volume of digester liquors and on condensation of 

steam. 

line shows the corrected curve, taking the overflow into consideration. 
The rapid increase in the condensation is a natural consequence of 
increasing the amount of cooking liquor, which has a high specific 
heat. 

In the tests employing various cooking periods the main influence 
on steam consumption was the heat lost by radiation, since the 
initial volumes of digester liquors were constant. The curve in 
figure 17 representing this effect has been drawn as a straight line 
to show only the general trend. It will be observed, however, that 
the platted points occur in two distinct groups. That the reaction 
between wood and caustic soda is of an exothermic or heat-generating 
nature may partly explain this arrangement. In the one group, 
representing the cooks of longer duration, the cooking reaction was 
31091°— Bull. 80—14 3 



34 BULLETIN 80, U. S. DEPARTMENT OF AGEICULTUBE. 

practically completed before the end of the cooking period (see 
analogous curves in figs. 12 and 13). This would result in relatively 
higher amounts of condensation, since no heat of reaction would be 
generated during the later stages of cooking. 1 The same explanation 
could apply to the cooks made at the higher pressures. 

The influence of higher cooking pressures on steam consumption 
results from the greater amount of steam required to heat the digester 
and its contents to the higher temperatures and the greater loss of 
heat by radiation at such temperatures. The initial volumes of 
cooking liquor did not vary. The condensation curve indicates that 
this effect was comparatively small in the tests. 

Like the tests varying the amount of caustic soda, those varying 
the initial concentration influence the steam consumption principally 
by the amount of liquor in the charge, which varies as shown by the 
true hyperbolic curve in figure 17. Hence, increasing the initial 
concentration decreased the condensation, as shown by the corrected 
curve in figure 17, which takes into account the overflow of the 
digester in cooks 25 and 26. 

In considering these results from a commercial standpoint it should 
be kept in mind that the experimental apparatus was comparatively 
small. On this account the heat or steam required for raising the 
temperature of the digester and for replacing heat lost by radiation 
per unit of digester capacity was far greater than would be experienced 
in mill operation. Hence, much less steam per pound of chips would 
be required in commercial operations than is shown by these curves. 
The effects of increased duration of cooking and increased pressures 
especially would be much less pronounced, since with these radiation 
is the more important factor. 

Aside from the direct cost of steam, the condensation is of impor- 
tance in another way. The tests have shown that decreased initial 
concentrations, other cooking conditions being constant, result in less 
severe cooking. It is to be expected that the decrease of concentra- 
tion throughout the cooking period, due to condensation, also tends 
to minimize the cooking effects in a similar manner. 2 

The use of superheated steam in cooking, the installation of larger 
digesters, the insulation or lagging of digesters, and the use of the 
minimum volume of cooking liquors at the start of cook are means 
frequently employed by pulp mills to reduce the condensation. 

i The condensation curve (liquor in digester— gallons) in fig. 3, which is typical for most of the individ- 
ual cooks in these experiments, also shows a greater rate of condensation at the end of the cook than al 
earlier periods except during the first hour when the pressure was being increased. Thiscan be accounted 
for only by the fact that heat, other than from the steam alone, was supplied to the digester during the 
earlier stages of cooking. As the cooking reaction is most vigorous at the beginning, it seems probable 
that the heat supplied was heat of react ion . 

* It is evident that the effects obtained In the tests varying the initial concentrations arc much leas pro- 
nomiced than would have been the case if the diluting effect of condensation had been absent. The auto- 
clave tests, for which data are given in Table 15, afford fairly conclusive proof of this. 



PRODUCING SODA PULP FROM ASPEN, 



35 



CHEMICALS PER TON OF PULP. 

The chemicals directly employed in the manufacture of soda pulp 
affect cost of production, in that the full amount of alkali charged to 
the digester can not be recovered, while the bleaching powder after 
being used is of no further value. The curves in figures 18 and 19, 
expressing the effects of the 
cooking conditions on the 
amounts of chemicals em- 
ployed per ton of air-dry, 
bleached pulp, were derived 
from the experimental data 
as explained on page 48, ap- 
pendix. The amounts shown 
are less than those generally 
employed in commercial prac- 
tice, for several reasons: (1) 
The yields of pulp are higher; 
(2) the losses on bleaching 
are less; (3) the amounts of 
chemical charged per pound 
of wood are less; and (4) the 
amounts of bleach required 
are less. Whether or not 
pulp mills can duplicate or 
approach these results, the 
general trend of the curves 
would not be affected. 



2200 



2000 



1800 



1600 



_) 1400 



1200 



1000 



800 



z 1800 

o 

*" I GOO 

at 

Ul 

a. 1400 

n 

a 1200 

z 

=J 

o 10 00 

o- I 

I 



9 ^-^°S 



.20 30 .40 

POUNDS NaOH PER POUND OF WOOD 



\ 








' 


} ■■' 


' 


. 


\ 
















\ 


I 




13 




10 

• 




j 






sr- 




"tt" 









2 4 6 8 10 12 
DURATION AT MAX. PRESSURE-HOURS 



SODA ASH. 



1400 



© 1200 



1000 









19 


W < 


17 






22 


21, 


20 













60 



70 80 90 100 110 120 
MAX.PRESSURE-PDS.PER SO. IN. 



1300 



1100 



The amounts of caustic 
soda and sodium carbonate 
charged to the digester in the 
several groups of tests have 
been calculated to show the 
equivalent amounts of com- 
mercial soda ash (58 per cent 
Na 2 0) per ton of bleached 
pulp produced. (Fig. 18.) 
Increasing the amounts of 
caustic soda charged per pound of wood obviously results in increas- 
ing amounts of ,soda ash per ton of pulp, and the decreased yields 
of pulp resulting from the more thorough cooking make the effect 
more pronounced. A bend is found in the curve at the point of 
maximum yield, since for amounts of caustic below this point the 
yields decrease rapidly and their influence on the amount of soda 
ash employed per ton of pulp becomes more apparent. 



Fig. IS.- 



40 SO 60 70 80 90 .00 110 
CONCENTRATION NaOH- GRAMS PER LITER 

-Effects of cooking conditions on amount of 
soda ash employed per ton of pulp. 



36 



BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 



600 




w 200 



S -10 



.20 .30 .40 
POUNDS NaOH PER POUND OF WOOD 



AYhen varying the durations and the pressures of cooking and the 
initial concentrations, the amounts of soda ash per ton of pulp were 
affected by yields alone, and the minimum amount is employed under 
conditions .which give the maximum yields. Increased durations, 

pressures, and concentrations 
afford decreased yields, and 
the amount of soda ash per 
ton of pulp consequently is 
increased. The platted point 
for cook 10 is not on the curve, 
due to the initial digester 
liquors for this cook having 
had about 3 per cent lower 
causticity than the other cooks 
in this group of tests. Lower 
causticities involve the use of 
a greater amount of soda ash 
for the same amount of caustic 
soda. 

BLEACHING POWDER. 

The curves in figure 19 show 
that increasing the amounts 
and concentrations of caustic 
soda and the durations and 
pressures of cooking result in 
all cases in decreasing the 
amounts of bleaching powder 
consumed. 

Yields do not influence the 
calculations, since the con- 
sumption per ton of bleached 
pulp depends on the per cent 
of bleach required and the 
bleaching losses. The ordi- 
nates for the curves represent 
bleaching powder of 35 per 
making the bleaching solutions 



500 

z 
o 
t- 400 


\ l$ 
















<r 


















m 300 

a. 

« 200 

Q 
Z 

=» 100 




\»IS 


















14 


13 


_«I2 


10 




1 



2 4 6 8 10 12 

DURATION AT MAX. PRESSURE- HOURS 



400 



300 



200 



100 



! 


r 
















V 


a i 


















20 1 


J9 


^18 


^17 





60 70 80 90 100 110 120 

MAX. PRESSURE-PDS. PER SO.. IN. 



200 r-=a 



40 50 60 10 80 90 100 110 
CONCENTRATION NaOH- GRAMS PER LITER 

Fig. 19.— Effects of cooking conditions on amount of 
bleaching powder employed per ton of pulp. 

cent available chlorine, and losses in 
are disregarded. 



COMBINED COST OF WOOD AND CHEMICALS PER TON OF PULP. 

The curves in figure 20 show costs for certain items in producing 
a ton of bleached pulp ('2,000 pounds air-dry basis) as influenced by 
variations in the cooking conditions. Curves marked A represent 
cost of wood alone; curves B, cost of wood and soda ash ; and curves C, 



PRODUCING SODA PULP FROM ASPEN. 



37 



cost of wood, soda ash, and bleaching powder. The vertical distances 
between curves A and B represent cost of soda ash alone, and those 
between curves B and C represent cost of bleaching powder alone. 

The cost values were obtained by calculations from the amounts 
of wood, soda ash, and bleaching powder consumed, based on the 
experimental results. 1 A 90 per cent recovery of the cooking chem- 
ical.-? charged to the digester was assumed in determining the amounts 



26 
24 

22 

in 
% 20 

-i 
_i 
o 18 

o 

I 16 

a. 14 

_i 

3 

o- 12 









































































> 


I 


<_ t 


-"" 


,. — ' 


^ 


"* 




v 


^ 


+^* 


•d 


A 






^ 


y^ 











.20 30 .40 

POUNDS NaOH PER POUND OF WOOD 







































































c 








































^ \,B. 


















A 













2 4 6 8 10 12 

DURATION AT MAX.PRESSURE-HOURS 



18 
v> 

K- 

w 1G 

o 
o 

14 
12 
10. 



E ■ 

J--"" — — ■""" 

A 



60 



70 80 90 100 110 120 
MAX PRESSURE-PDS. PER SO. IN. 



c 

6 . . —' 

A 



40 50 60 70 80 90 100 110 
CONCENTRATION NaOH- GRAMS PER UTER 



Fig. 20.— Effects of cooking conditions on cost items per ton of pulp. A, wood; B, wood and soda 
ash; and C, wood, soda ash, and bleaching powder. 

of soda ash consumed or lost per ton of pulp. The basic units for 
costs are assumed average values as follows: 

Wood, $9 per solid cord (100 cu. ft.); soda ash (58 per cent Na 2 0), 
$1 per 100 pounds; bleaching powder (35 per cent available chlorine), 
$1.55 per 100 pounds. 2 The bone-dry weight of aspen wood is taken 
as 26.68 pounds per cubic foot of clear wood, green volume. 

1 These amounts were calculated by interpolating from the yield curves (fig. 4), the loss on bleaching 
curves (fig. 10), and thecurves for soda ash and bleaching powder employed per ton of pulp (figs. 18 and lu), 
and not from actual test data. On this account platted points have been omitted. 

2 Reasonable maximum, average, and minimum values for a "solid cord" of aspen f. o. b. mill are 811, 
$9, and 86, as determined from statistical reports received from a number of mills. Correspondence with 
pulp manufacturers brought the information that reasonable maximum, average, and minimum unit 
costs as defined above may be assumed with a fair degree of accuracy as follows: For soda ash, 81.20, SI, 
and $0.85; for bleaching powder, $2.05, $1.55, and $1.10. These values do not depend upon market fluctua- 
tions alone, but vary through the range given, due largely to differences in freight charges lor mills in 
different localities. The actual selling price of "58 per cent" soda ash is 10/18 greater than the manufac- 
turer's or market quotations, since the latter are based on the old standard of "48 per cent" soda ash. 



38 BULLETIN 80, U. S. DEPARTMENT OF AGRICULTUPE. 

With increasing amounts of caustic soda in the digester charges 
the cost due to all three factors is decreased until the point of maxi- 
mum yield of good pulp is attained, after which the total costs 
increase, due to the increasing amounts of wood and of soda ash 
consumed. The decreasing cost of bleaching powder only partialty 
offsets the increase due to the other two factors. 

With increasing durations the effect is practically the same, so far 
as wood alone is concerned, except that the increase in its cost for 
higher durations is not so pronounced as with increasing the amounts 
of caustic soda. The soda-ash costs alone are practically constant, 
and hence increase the wood costs by a constant amount. However, 
as the durations increase, the bleaching-powder costs decreased suffi- 
ciently to overcome the effect of increasing wood costs. After the 
minimum duration for successful cooking (as determined by yields) 
has been exceeded, the decrease in total cost is very small, and would 
not be sufficient to offset increased costs incident to the time element 
discussed previously. 

For variations in the pressures of cooking, the influence of bleaching- 
powder costs is especially marked. The minimum costs due to wood 
and soda ash result from the use of the lower pressures. When 
bleaching is considered, the minimum cost is obtained by using 
medium pressures, although the increases for the higher pressures are 
very small. 

Combined costs for the three factors are practically unaffected by 
variations in the initial concentrations, but if bleaching is omitted the 
costs of wood and soda ash are larger with the higher concentrations. 

All of the diagrams show that of the three cost factors considered, 
wood is of the most importance and that bleaching powder is more 
influential than soda ash in determining total costs. Increases in 
costs of wood and soda ash with increasing severity of cooking are, 
in all cases, offset, to a greater or less extent, by decreases in bleaching- 
powder costs. If maximum or minimum values x had been used for 
either wood, soda ash, or bleaching powder, instead of the average 
value, or if a different percentage recovery for the soda ash had been 
assumed, the general effects would not be changed, although they 
might become more or less pronounced. 

SUMMARY. 2 

(1) The amount of caustic soda per pound of wood, the duration 
of cooking, the pressure or temperature of cooking, and the concen- 
tration of the cooking chemicals employed in the production of soda 

1 See footnote, p. 37. 

2 The more general statements in the summary will be found to coincide in a greater or less degree with 
previously existing opinions, a fact not surprising when it is remembered that the soda process has been 
carried on for half a century. On the other hand, satisfactory evidence and data substantiating these 
opinions have not been available. The present investigation affords such information, as well as a basis 
for more specific conclusions. 



PRODUCING SODA PULP FROM ASPEN. 39 

pulp influence the yield and properties of the pulp by influencing the 
severity of the cooking reactions. 

(2) Severity of cooking is an effect mainly of the amount of caustic 
soda consumed per unit of wood. Increasing the amount or concen- 
tration of the chemical or the pressure of cooking produces a quicker 
reaction and hence one more complete in a given length of time. 
Increasing the duration results in a more complete reaction because 
of the longer time allowed for the available caustic soda to be con- 
sumed. 

(3) Greater severity of cooking is accompanied by a decrease in 
the yield of crude pulp, and usually of screened pulp. If screenings 
are present in considerable quantity (due to incomplete cooking), 
more thorough cooking increases the yield of screened pulp. 

(4) The properties of the pulp are influenced by greater severity 
of cooking as follows : 

(a) Shives are decreased in mimber or eliminated. 

(6) Bleaching is rendered more easy and the loss on bleaching becomes less. 

(c) The strength may either decrease or increase, depending upon which cooking 

condition is varied and the degree of variation. 

(d) The color of the unbleached pulp becomes lighter within certain limits, 

beyond which it may, under certain conditions, become darker. 

(5) A good indication of the severity of cooking is the appearance 
of the individual fibers when examined under the microscope. 

(6) The decreased yields resulting from more severe cooking result 
in a greater cost of wood and soda ash per ton of pulp. As a rule, 
the smaller cost of bleaching powder incident to the more easily 
bleached pulp produced by thorough cooking only partially offsets 
the greater cost of wood and soda ash. 

(7) While the amount of bleach required decreases with increasing 
severity of cooking, a point is soon reached where the decrease in 
bleach required is not commensurate with the decrease in yields. 

(8) Increasing the initial amount of digester liquor increases the 
condensation and steam consumption (and hence the cost) because 
of the greater volume to be heated; increasing either the duration 
or pressure has a similar effect because of the greater losses of heat 
by radiation. 

(9) Yields (bone-dry basis) of well-separated unbleached pulps as 
high as 56 or 58 pounds per 100 pounds of wood can be obtained from 
aspen if the wood is of the best quality. Yields of from 54 to 55 per 
cent were obtained which required only from 10 to 11 per cent of 
bleach. The variation in yields obtained by changing the cooking 
conditions was from 46 to 58 pounds per 100 pounds of wood charged, 
or about 26 per cent based on the lowest yield. 

(10) Minimum total durations of from 3 to 4 hours may be success- 
fully applied to the cooking of aspen for bleaching pulps, provided 
the other cooking conditions are properly maintained. 



40 BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 

(11) Aspen may be successfully cooked with a minimum of from 
20 to 25 pounds of caustic soda charged per 100 pounds of wood. 
The amount of this chemical actually consumed in the production 
of well-cooked bleaching pulps varies from 18 to 24 pounds per 100 
pounds of wood. 

PRACTICAL VALUE OF RESULTS. 

The experiments discussed in this bulletin have shown in detail 
the effects of certain cooking conditions on the yields and properties 
of the resultant pulp, on the efficiency of the cooking chemicals, and 
on various items affecting costs of production. From a study of 
these results it should be possible for a mill operator so to regulate 
the cooking process as to secure the largest possible yield of pulp of 
the desired quality at a minimum cost for chemicals, fuel, labor, and 
overhead charges hi so far as the operation is affected by the cooking 
conditions considered. 

The clear, sound wood used in the experiments afforded yields of 
good pulp from 10 to 25 per cent higher than the better run of the 
yields reported by pulp mills. Moreover, some of these experimental 
yields were obtained with shorter cooking periods and less chemicals 
than are employed commercially. Although the laboratory results 
may not be equaled in mill practice, the possibility of greatly 
increased efficiency in the process of converting wood into soda pulp 
is indicated. 



APPENDIX. 



ASPEN AS A RAW MATERIAL FOR PAPER PULP. 

DISTRIBUTION AND CHARACTERISTICS OF THE TREE.' 

Aspen (Populus tremuloides Michx), or quaking aspen, as it is sometimes called, is 
one of the most widely distributed and best-known American trees. Together with 
the closely related European species, Populus tremula Linn., from which paper pulp 
of excellent quality is also prepared, it encircles almost the entire globe. In America 
aspen extends from Labrador to Alaska and southward to Tennessee and Arizona. 
Yet it occurs scatteringly, and pure stands of any extent are comparatively rare. For 
this reason it is not possible to give even approximately the present total stand. In the 
western forests, notably those of Utah and western Colorado, there are vast quantities 
which will doubtless be an important source of future supply. In the past New Eng- 
land furnished most of the aspen pulpwood, and although the supply there is badly 
depleted, considerable quantities yet remain in certain regions, notably in northern 
Maine. 2 

Aspen is a very rapid grower and quickly covers burned or logged-over lands. How- 
ever, it is comparatively short-lived, and the larger trees suffer severely from fire, 
windshake, insects, and fungi. In fact, aspen is defective from decay to a greater 
extent than any other commonly used pulpwood, except perhaps balsam fir. The 
trees ordinarily used for pulpwood are from 5 to 14 inches in diameter. If grown in 
close stands, the trunks are fairly free from knots and limbs. Logging is compara- 
tively easy. 

Aspen wood after cutting is also susceptible to fungous attack unless kept very dry. 
It is particularly perishable in contact with the soil. The ability of the wood to season 
rapidly, especially after being barked, is of much advantage. Nevertheless, mills 
which store a year's supply or more in open yards undoubtedly have a large proportion 
of their older wood affected. The general opinion is that "old wood" produces infe- 
rior pulp and lower yields. 

PROPERTIES AND STRUCTURE OF THE WOOD. 

The wood of aspen is soft, light in weight, not strong, and close grained, but with 
numerous minute, open ducts. The medullary rays are very thin and hardly distin- 
guishable with the naked eye. The color is light brown, the sapwood almost white and 
very thick, often representing 25 to 30 layers of annual growth. In the green or freshly 
seasoned material, however, the difference between heartwood and sapwood is in most 
cases scarcely appreciable. A cubic foot of air-dried wood usually weighs from 25 to 

30 pounds. 

i — i 

1 A more complete discussion of the silvical characteristics of aspen is given in Forest Service Bulletin 
93, The Aspens; Their Growth and Management, by W. <!. Weigle and E. II. Frothingham, 1911. 

2 Forest Service Bulletin 9:!, pp. 13 and 17, lull. 

41 



42 BULLETIN 80, U. S. DEPARTMENT OP AGRICULTURE. 

Determinations ' made on sound sticks of aspen varying from 8 to 10 inches in diame- 
ter showed about 62.8 per cent of cellulose. Muller, quoted by Clapperton, 2 gives the 
following analysis ;i for the poplars: 

Per cent. 

Cellulose , 62. 77 

Resin 1. 37 

Aqueous extract 2. 88 

Water 12.10 

Lignin 20. 88 

100. 00 

Since bleached pulp is very nearly pure cellulose, the maximum yield obtainable 
could not be appreciably higher than 63 per cent. 

Aspen wood is made up of three types of structural elements — fibers, vessels, and 
parenchymatous tissue. The latter comprises the medullary ray cells and the rather 
scantily developed parenchyma cells at the end of the year's growth. The structure 
is shown in Plates VIII and IX. In Plate VIII, figure 1, the long tubes running the 
length of the picture are the vessels; cross sections of the medullary rays can be seen 
scattered among the fibers as dark vertical "plates," one cell in width and several in 
height. The ray cells are characterized by exceedingly thin walls, and when the 
wood is cooked for pulp these cells readily dissolve. The vessels are more resistant to 
chemical attack than the parenchymatous tissue, and the fibers, because of their 
relatively thick walls, are least affected by the cooking process. It is also possible 
that the cellulose constituting the fiber walls is more resistant than the cellulose of 
the other elements. In Plate IX, figure 2, the middle lamella or intercellular sub- 
stance appears as a black line between the adjacent walls of the elements. This is 
dissolved in the process of cooking for paper pulp. 

Aspen fibers are comparatively short. Examples of long-fibered woods used in 
paper making are spruce, hemlock, and balsam fir, and of medium-length ones tulip 
tree, sweet gum, and Cottonwood. The actual dimensions of aspen fibers vary a 
great deal with the tree and the part of the tree from which secured. Forest Service 
measurements 4 of a large number of fibers of aspen wood showed a range of from about 
0.5 to 1.6 mm. in length and an average length of 1.0 mm. 5 

PULPWOOD CONSUMED. 

At the present time soda, sulphite, sulphate, and mechanical pulps are made from 
aspen and other poplars, but the soda process has always used these woods in by far 
the greater amounts, and they continue to form the chief pulpwood supply for this 
process. The other processes of pulp making have been applied to the poplars within 
recent years only, although it was known 20 or 30 years ago that they could be ground 
for mechanical pulp and could be reduced without difficulty by the sulphite process 
to an easy-bleaching pulp. The properties of the wood and the yields and qualities 
of the pulp made from it, combined with the proximity of an adequate supply and 
its relatively low cost, made this the best wood obtainable for the manufacture of soft, 
easy-bleaching soda pulp. 

i Forest Service Bulletin 93, p. 7, 1911. 

1 Practical Papermaking, p. 43, 1907. 

a This analysis makes no mention of the ash. According to Sargent (Tenth U. S. Census Rept., Vol. IX) 
the ash in aspen varies from 0.31 to 0.76 per cent, with an average of 0.55 per cent, of tho air-dry wood. See 
this report also for further data on the chemical composition and properties of aspen. 

« Forest Service Bulletin 93, p. 7, 1911. 

6 One millimeter is equivalent to approximately one twenty-Al'th of an incu. 



PRODUCING SODA PULP FROM ASPEN. 



43 



Table 5. — Consumption of poplar pulp ioood and of all pulpivoods in the United States 
for years 1899 and 1905 to 1910, inclusive. 



Year and process. 


Domestic 
poplar. 


Imported 
poplar. 


Total 
poplar. 


All pulp- 
woods. 


Ratio 
djmestic 
poplar 
to total 
poplar. 


Ratio 
total 
poplar 
to all 
pulp- 
woods. 




1910.1 


Cords. 
11,613 
2 703 
303, 401 


Cords. 
1,834 


Cords. 
13,417 
2 703 
346, 926 


Cords. 
1,180,598 
3 2,257,881 
655, 827 


Per cent. 
86.4 
100.0 
87.5 


Per cent. 




03 




43,525 


53 




1909.1 






315,717 


45,359 


361,076 


4,094,306 


87.4 


8.8 




17,905 

2, 930 

282,041 


3,025 
'""22," 597" 


20, 930 

2, 930 

304,638 


1,246,121 

* 2, 183,984 
571,502 


85.6 
100.0 
92.6 














1908.1 






302,876 

16, 734 
3,734 

259, 090 


25,622 


328,498 


4,001,607 


92.2 


8.2 




2,168 
3,023 
17,462 


18,902 

6,757 

276, 558 


1,117,428 

1,739,282 

490, 243 


88. 
55. 3 
93.6 








Soda -. 






1907.1 






279, 564 


22, 653 


302,217 


3,346.953 


92.5 


9.0 




16, 903 

1,536 

333, 703 


2,620 


19, 523 

1,536 

350, 881 


1,361,302 

2, 059, 496 

541,862 


86.5 
100.0 
95.0 


1 4 


Sulphite 






17, 178 






1900.5 






352, 142 


19, 798 


371,940 


3,962,660 


94.7 


9.4 




10,475 


2,129 


12,604 


1,197,780 

1, 958, 619 

504, 777 


82.8 






.0 


Soda 


300, 445 


15,421 


315,866 


95.1 






1905.6 






310,920 


17,550 


328,470 


3,661,176 


94.6 


9.0 




8,592 


2,800 


11,392 


1,096,794 

1, 630, 393 

464, 936 


75.4 


1.0 
.0 




Soda 


290, 583 


20,083 


310,666 


93.5 


66 8 




18997 






299, 175 


22, 883 


322,058 


3, 192, 123 


92.9 


10.1 


Total 


8 236, 820 


s 20, 133 


« 256, 953 


1,986,310 


92.3 


V> 9 







1 Bureau of the Census Circulars, Forest Products No. l.Pulpwood Consumption (for respective years). 

2 Includes 78 cords reduced by the sulphate process. 

3 Includes 10,188 cords reduced by the sulphate process. 
* Includes 38,000 cords reduced by the sulphate process. 

s Forest Service Circular 120, Consumption of Pulpwood in 1906. 

6 Forest Service Circular 44, Wood used for Pulp in 1905. 

7 Twelfth Census Bulletin 99, Manufactures: Paper and Pulp, Sept. 30, 1901. 

8 Used exclusively by the soda process. 



44 



BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 



Table 6. — Cost of poplar pulp wood and of all pulpwoods at United Stales mills in 1907, 

1908, and 1909. ! 



Quantity. 



Total cost. 



Average 

cost per 

cord. 



1909. 
Rough wood: 

Domestic poplar 

Imported poplar 

Total poplar 

All pulpwoods 

Peeled wood: 

Domestic poplar 

Imported poplar 

Total poplar 

All pulpwoods 

Rough and peeled wood: 

Domestic poplar 

Imported poplar 

Total poplar 

All pulpwoods 

1908. 

Domestic poplar 

Imported poplar 

Total poplar 

All pulpwoods 

1907. 

Domestic poplar 

Imported poplar 

Total poplar 

All pulpwoods 



Cords. 

13,953 

2,984 

16, 937 

2,219,083 

288, 923 

22, 638 

311,561 

1. 113,997 

302,876 

25,622 
328, 198 

1,001,607 



279,564 

22,653 

302, 217 

3,346,953 



352, 142 

19, 798 

371,940 

3,962,660 



Dollars. 

72, 555 

24,469 

97,024 

17,608,736 

2, 337, 461 

179,019 

2,516,480 

12,169,393 

2,410,016 

203,488 

2,613,504 

34,477,540 



2, 237, 631 

182, 143 

2, 419, 774 

28,047,473 



2,763,889 

167,039 

2,930,928 

32,360,276 



Dollars. 
5.20 
8.20 
5.72 
7.94 

8.09 
7.91 
8.07 
8.61 

7.96 
7.94 
7.95 
8.62 



8.01 
8.04 
8.00 
8.38 



7.85 
8.44 



8.17 



1 Bureau of the Census Circulars, Forest Products No. 1, Pulpwood Consumption (Tor respective years). 
Prices quoted are based on f. o b. mill deliveries. 
1 Includes 368,527 cords of rossed wood at an average cost of $12.75 per cord. 

While there are no statistics of the consumption of aspen pulpwood alone, the Census 
figures ' for the consumption of "poplar" are of interest. The woods grouped under 
this name consist of several species of the true poplars, of wldch aspen is by tar the most 
important, and doubtless include also a small amount of "yellow poplar" or tulip tree 
(Liriodendron tulipi/era Linn.). The poplars collectively stand third in the amount 
cut for pulpwood, being exceeded only by spruce and hemlock. Table 5 shows the 
amount of poplar pulpwood used, by processes, in 1899 and each year from 1905 to 
1910, inclusive. The cost of poplar per cord in 1907, 1908, and 1909 is shown in Table 
6. The average cost per cord for poplar pulpwood did not change materially during 
the period 1907 to 1909, though the average cost per cord for all pulpwoods steadily 
advanced. 

PAPER PULP FROM ASPEN. 

CHARACTERISTICS AND PROPERTIES. 



Aspen soda pulp, when unbleached and dry, is a very light brown or light reddish- 
brown much resembling ordinary blotting paper. While fairly tenacious, the pulps are 
usually very soft and bulky, whether bleached or unbleached. The softness ot the pulp 
may be partly due to the fact that its natural resin content is normally very low (0.05 
per cent) as compared with ordinary sulphite pulp (0.5 per cent). Aspen soda pulp 
is easily bleached to a good white color, though in some cases there may be a slight 
reddish tinge. For well-cooked pulp very low amounts of bleaching agents are 
required, and the loss on bleaching (from 6 to 10 per cent in commercial practice) 
is comparatively small. The following table by Griffin and Little 2 affords a com- 

1 For statistics on the consumption of poplar pulpwood by Canadian mills, see bullet ins 12, 26, and 30, of 
the Forestry Branch, Canadian Department of the Interior, 1909-1912. 
s Chemistry of Papermaking, p. 280, 1894. 



Bui. 80, U. S. Dept. of Agriculture. 



Plate VIII. 




^ a 

O Ph 
O « ~ . 



<Q a 




o ,2 

O Q. T3 

_l uJ o> 

p^ ■- 

zQ « 

HI ~ 

O '_, 

z > 

< - 

I— « 



Bui. 80, U. S. Dept. of Agriculture 
SPRING WOOD 



Plate IX. 
SUMMER WOOD 




PRODUCING SODA PULP FROM ASPEN. 



45 



parison between the amounts of bleaching powder required for pulps from poplar 
(including aspen) and for other pulps: 

Table 7. — Amount of bleaching powder required for commercial pulps. 



Kind of pulp. 


Bleaching 

powder per 

100 pounds 

of pulp. 




Pounds. 
18-25 
12-15 
10-15 

15-25 
14-20 






Sulphite spruce 



The individual fibers in aspen soda pulp are of the following dimensions:' Length, 
from 0.67 to 1.49 mm., averaging 0.99 mm.; breadth at the middle, from 0.01 to 0.03 
mm., averaging 0.02 mm. ; appn >ximate thickness of cell walls, 0.002 mm. ; ratio of length 
to breadth, 50:1. The fibers are slender, gradually tapering to needle-pointed ends. 
They are pliable and mostly curved, although many are nearly straight. While 
sometimes twisted and often swollen in nodes, with slight constrictions, they are 
never badly tangled or knotted. Aspen fibers tend to be more nearly circular in cross 
section than those from conifers. Other distinguishing characteristics are the medium 
length of the fibers and the presence, except in "overcooked " pulps, of remnants of the 
larger wood vessels and parenchymatous tissue. The vessel walls have closely packed 
bordered pits with hexagonal contour, and the inside walls are not marked with spiral 
thickenings, as is the case with some species. The vessel ends have open pores without 
gratings, which distinguishes aspen pulp from that of the tulip tree or yellow poplar 
sold in European markets under the name "Amerikanische Aspenzellulose." 2 

YIELDS. 

The yields reported by a number of American soda-pulp mills operating on aspen 
and other woods are given in Table 8. 

Table 8. — Yields of soda pulps reported by various mills. 3 



Species of wood. 



Yield per 
cord.* 



Poplar: 

100 per cent donestic. 
Do 



Do. 
Do. 



59 per cent domestic, 41 per cent imported. 

100 per cent domestic 

Do. 



Pounds. 

1,000 
1.040 
1,050 
1.050 
1,075 
1,102 
1,139 
1,144 
1,153 
1.161 
1.170 
1.191 
1,200 
1,209 

1 The dimensions and characteristics were determined microscopically from 52 separate fibers from the 
26 different cooks made in these experiments. No effort was made to select extremely long or extremely 
short fibers. See also photomicrographs of pulps, Plates II to VII. 

2 Litchauer, Zentr. f. d. Oesterr.-ung. Papierin lustrie, p. 822, vol. 23, 1905. 

3 Each value is the report of 1 mill, received during the period 1907-1909. 

< On the percentage basis the yields of soda pulp from poplar also vary widely. Reid (Jr. Soc. Chem. 
Ind., pp. 273-276, vol. 5, 1S86) reports a yield of 41 per cent. De Cew (Jr. Soc. Chem. Ind., pp. 561-563, vol. 
26,1907)cites a yield of 44 per cent, or 1,150 pounds per cord, from large-tool li aspen. Sindall ( Paper Tech- 
nology, p. 201, 2d ed. 1910) mentions a yield of 52 per cent, which is unusually high for commercial 
practice. 



33 per cent domestic, 67 per cent imported . 

100 per cent domestic 

59 per cent domestic, 41 per cent imported . 

100 per cent domestic 

91 percent domestic, 9 percent imported.. 

100 per cent domestic 

90 per cent domestic, 10 per cent imported. 



46 BULLETIN 80, U. S. DEPAETMENT OF AGRICULTURE. 

Table 8. — Yields of soda pulps reported by various mills — Continued. 



Species of wood. 



Yield per 
cord . 



Poplar 11 per cent and pine 89 per cent 

Poplar 91 per cent and chestnut 9 per cent 

Poplar 75 per cent and gum 25 per cent 

Poplar 95 per cent and gum 5 per cent 

Poplar 12 per cent, pine 88 per cent, and gum small amount 

Poplar 3 per cent, pine 25 per cent, and maple 72 per cent 

Poplar 32 per cent, pine 52 per cent, and hemlock 16 per cent 

Poplar 13 per cent, pine 1 per cent, and chestnut 86 per cent 

Poplar 7 per cent, pine 43 per cent, maple 45 per cent, and basswood 5 per cent 

Poplar 9 per cent, pine 34 per cent, maple 19 per cent, beech 19 per cent, other hard woods 19 

per cent 

Poplar 56 percent, maple 7 percent, and basswood 37 percent 

Poplar 40 per cent; birch, maple, beech, and basswood 

Poplar 30 per cent, cottonwood 30 per cent; maple, buckeye, willow, and lime 10 per cent each. . 



Pounds. 

1.IIIIO 

800 
1,000 
1,139 

985 
948 
862 
800 
1.014 

794 
1,043 
1,160 
1.000 



The several yields were all determined from the amounts of wood consumed annu- 
ally by each mill and the total production of pulp in the same time. The yields 
represent air-dry, bleached pulp, except for a few of the mills which used coniferous 
woods, together with the poplars. 

The experimental work of the Forest Service shows that yields of over 55 per cent 
(bone-dry basis) of unbleached pulp (see Table 11) can be obtained. Even the lowest 
yield of good unbleached pulp was not less than approximately 45 per cent. A yield 
of 55 per cent amounts to over 1,450 pounds of bone-dry, unbleached pulp, or over 
1,600 pounds of air-dry, bleached pulp, per 100 cubic feet of solid wood. The average 
128-foot cord of peeled aspen contains approximately 90 cubic feet of solid wood, 1 
and on this basis would produce 1,440 pounds of air-dry, bleached pulp. 

It seems evident, therefore, that considerably higher yields can be obtained from 
aspen than are secured in commercial practice. One of the many reasons for the 
lower yields of the commercial plants is probably the quality of the wood. 2 In the 
Forest Service tests the wood used was clear and sound, all defective material having 
been culled. 

USES. 

The principal use of soda poplar or aspen pulp is in the bleached form for such 
papers as book, magazine, antique, coated, lithograph, map, card, cover, common 
envelope, and writing, and wood blotting papers; also the soft, bulky papers some 
times required for special purposes. In making these papers longer-fibered pulps 
that is, bleached rag or sulphite wood pulps, are mixed with the soda pulp in various 
proportions up to 80 per cent of the whole. These other fibers are added mainly for 
the purpose of strengthening the soda pulps, and their proportion in the mixture 
depends upon the desired quality of the product. The use of considerable amounts 
of soda poplar pulp is favored in some cases because it imparts to the sheet of paper a 
bulkiness and opacity not readily obtainable with ordinary sulphite or rag pulp alone. 
The addition of the long-fibered pulps tends to increase the cost of the products, 
but gives them more lasting qualities. These mixed pulps lend themselves with 
particular case to the various paper-making operations, such as sizing, coloring, 
beat ins,', and running on the paper machine. 

The amount of various kinds of wood pulps used in the United States in 1909 and 
1899 is shown in Table 9. 

1 Forest Service Bulletin 36 (rev. ed., 1910), p. 113, Woodman's Handbook, by II. S. Graves and E. A. 
Ziegler; also "Factors influencing the volume of solid wood in the cord," by R. Zon, Forestry Quarterly, 
p. 126. No. 4, vol. 1. 

2 In some earlier experiments by the Forest Service considerably lower yields were obtained, which were 
attributed to the inferior quality of i lie v ood. See Table 15. 



PEODUCING SODA PULP FROM ASPEN. 



47 



Table 9. — Amounts of mechanical, soda, and sulphite wood pulps used in the United 

States. 



Kindo 


pulp. 




Total 


pulps. 




Imported pulps. 


1909 > 


1899 




1909 


i 




Tons. 
1,323,000 
304, 000 
1,200,000 


Per cent. 
47 
11 
42 


Tons. 
586, 374 
171,959 
416, 230 


Per cent. 
50 
IS 
35 


Tons. 
119,500 

9,500 1 
172, 400 


Cost. 

S2, 723, 000 
398 000 






8 142 000 








Total 


2, 827, 000 


100 


1,174,563 


100 


301,400 


11 263 000 







1 Bureau of the Census— Paper and Wood Pulp Statistics; preliminary report for 1909, issued Apr. 26, 
1911, p. 3. 

2 Bureau of the Census— Bulletin 99 of the Twelfth Census, pp. 10, 12, 1901. 

RECORDS OF THE SERIES TESTS. 

Tables 10 to 14 give the data for the several groups of tests in which the cooking 
conditions were varied in series. 

EXPLANATION OF DATA. 

The following column headings may need explanation: 

Water in chips. — The quantity of water or moisture in the chips as charged is ex- 
pressed in percentage of water based on the calculated bone-dry weight of the chips. 

Initial concentrations of digester liquors. — The caustic soda (NaOH) and the sodium 
carbonate (Na 2 C0 3 ) concentrations are determined by analysis of the stock soda 
solution, and are calculated on the basis of total liquid in the charge, including mois- 
ture in the chips. The total sodium oxide (Na 2 0) is calculated from the proportions 
of NaOH and Na 2 C0 3 , each reduced to the sodium-oxide basis. Grams-per-liter 
concentrations may be converted into the equivalent pounds per gallon by multi- 
plying by 0.00834. What is sometimes erroneously called percentage concentrations 
may be obtained by dividing grams-per-liter concentrations by 10. 

Causticity of liquor. — This represents the ratio of sodium oxide in the caustic soda 
to the total sodium oxide. 

Initial volume of digester liquors. — The digester liquors consist of the stock soda solu- 
tion and water charged, together with the water in the chips as charged. 

Chemicals charged. — The quantities of the several chemicals charged are their dry 
weights based on the chemical formulae indicated. 

Duration of cooking. — Compare data with figure 3. 

Apparent condensation. — This is obtained by subtracting the amount of digester 
liquors at the start of the cook from the amount of liquid in the digester (as read from 
a water gauge) just before relieving the pressure, and blowing the digester at the end 
of the cock. It affords a rough measure of the amount of water condensing from the 
steam used for cooking. 

Yields. — The yields of total crude pulp, screenings, and screened pulp are calcu- 
lated to a bone-dry basis, and are expressed as a percentage of the calculated bone- 
dry weight of the chips. The total crude pulp is the total fibrous material and un- 
cooked chips blown from the digester. 

Yields of pulp per solid cord. — In calculating yields to pounds per cord of wood a 
"solid cord" is considered equivalent to 100 cubic feet of solid wood, green volume, 
knot free. For the aspen tested, the calculated bone-dry weight per "solid cord " was 
2,668 pounds. The yield of bleached pulp, which is given on the air-dry basis (10 per 
cent moisture), is computed by deducting the loss on bleaching and considering 90 
pounds of bone-dry pulp equal to 100 pounds of air-dry pulp. 



48 BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 

Color ratings. — These are numerical expressions of the colors of the unbleached 
pulps, and were determined on machine-made sheets by means of a tint photometer, 
according to the method described on page 54. 

Average strength. — The strength tests were conducted on machine-made sheets of 
unbleached pulp in the air-dry condition. 1 The methods of testing are described on 
page 54. 

Bleach required. — This represents the parts of bleaching powder (35 per cent availa- 
ble chlorine) required to bleach 100 parts bone-dry weight of unbleached pulp to the 
commercial white color. 

Loss on bleaching. — This is based on the calculated bone-dry weight of unbleached 
pulp lost when bleaching it to the commercial white color, with the stated per cent of 
bleach. 

Causticity of black liquor. — This was determined by analysis, and is the ratio of the 
sodium oxide in the caustic soda existing as such in the black liquor to the total sodium 
oxide in the black liquor. The latter represents the total titratable alkali in the ash 
resulting from calcining the black liquor. 

Efficiency in the use of NaOH. — This is the ratio of the amount of caustic soda actu- 
ally consumed during the cooking operations to the amount of caustic soda originally 
in the charge. It is calculated from the causticity of the black liquor, assuming that 
the soda chemicals in the black liquor are all titratable as sodium carbonate, after the 
liquor has been reduced to an ash. 

Wood, soda ash, and bleach employed per ton of pulp. — The volume of wood is based 
on the average bone-dry weight of aspen used in the tests (2,668 pounds per solid cord). 
The soda ash represents the total soda ash of 99.1 per cent purity (58 per cent Na 2 0) 
necessary to furnish the chemicals employed in cooking, assuming that no loss of 
alkali occurs in causticizing. The bleaching powder represents the dry weight of this 
chemical, losses in making the bleaching solutions being disregarded. 

i The failure of the Schopper tests to show even relatively uniform variations in the strength of pulp as 
affected by changes in the cooking conditions can not be explained unless that the pulps were not suitable 
for these tests. 



PEODUCING SODA PULP FROM ASPEN. 



49 



•(sisBq Xjp-anoq) 
sdiqo jo punod aad 
uojtesuapnoo inaacddy 



•qoui 
ajcnbs aad }apn Jajsa2 
-ip in ainssajd lUEa^s 



•samjejad 
-inaj Stn^ooo umunxejq; 



•qoni ajBnbs jad a.ms 
-sajd a8ne3 umunxBj^ 



•amssajd 
o§nB§ uimmxBin i y 



aans 
-saidaSriBS OJ92 ^y 



'IBjox 



£ as. 



"O^N TO°X 



' £ O0»BN 



"HO^N 



•(siscq jfip-anoq) sdpqo 
jo ' punod Jad saoribii 
jajsaSip jo aran[Ox\. [Bigirai 



A^pijsnBg 



•O^NPnox 



' 8 OO^N 



'HO^N 



sdiqo ra jaijB^ 



•(siseq ^jp-auoq) 
paSiBqo sdiqo jo iqSiaAV 



•Bo 

si p 
0° 



3 £ 



• 2 M t. 






:.3c< 



CO O OMiCrtOCl 

oo as r-u:NiOH© 

^OS O OlOOOiQX 



«y :q ^^i^;^^^ £S 



OOOO 0:00000 
„ t~- t-~ t^- co •>- t-* t-- t^ r- 



' X 00 00 t^ 00 00 00 00 00 
- co co co co co co co co ro 

coooco co co co co co co 



c<: o oo oo 
os o o oo o 



^ooo oooooo 

j^r^t^t^ d d d d cd 'sO 

o£tNTT « tN t}- (N tN O 

S 6 ' ' 

^ooo oooooo 

»fe oo oc oo t^t^r^t^t^t^ 

oooo oooo^r-- 

^cOwt^- t^ O OS CJ i-f O 

^OO^H i-H 00 CO t^ CO (T-i 

JNiOt- tD t^- iO CO -f 00 

JgCNt-CM iCCOOOOON 

«C- HO CN ClCiO^OC) 

^ 01 s - oo ?^ ^ o ■^t-o o 

^io'i<o oi >^ o <3>i o ^ 

H CO CM <N GO <30 <30, ^* ©i >-h 

•OJOJCO M-tOOtOON 

"gcooSo o oi ci n c ci 

£2 iO co ^ »c io t co o: oi 

go 

^'•OOICO »i »H ■<*< t>» 01 03 

o ■ • • 

t^t^cO 1>- t-- r* t^- CO CO 

<" , CO t^ CO OOl^fH^OO 

fe CO CO "^ ^PCOt^t^-^CO 

-J .-- CO CO CO O © iO «3 CO CO 
fc: -^. 

J5 

^ .NNOO HHiONNH 

. £ co co co co co co co' ti^ -^ 

S3 
J3 

»> ,OWN NOxOON 

. fe 00 O OS OQWrtQoi 

S* t ~j t*. 00 t~ XMNNXN 

_cs 

kiJOHO co *c co oo ■**■ ■■* 

V fi 

D, S^IOJO OOOSOSOSOSOS 



IN t6 



O!00 

•*t^ 

OS OS 



CO f 
•O CO 

to to 



•dci 



oo 

QQ 



OS-H 

oo os 



COOOS co os o o o o 

; ~h -* o cooooosoo 

^ > os os os Qoidosdo 

COCOCO ~« CO -3- CO •* •* 



OOl 
Oos 



r* ^ ^h osco to os - 



Q a o a a o jr; 






"ON 3[000 



M 



31091°— Bull. 80—14- 



hnm -*r io co t>* cc o> 



lOtCOOcDiO 
CN CO N lO CI 



iO »0 CD -^ CN 



pooo o 



5 £ 



X A y. s -r 

CO CO CO CO CO 
COCO COCOCO 



o o o o o t: 
o o o o o 

„ rt — -H H J- 

I* 

o 

oaooo -g 

OS N ti « '^' ^2 

CO •<»< (N •* •* ^ 

s 

s 

ooooo "* 

ostiO'Jci "* a 

■ °M 

(M CO tOO GO A ^ 

00 00 t^ OS l^ OS -^ 

OS OS OS O OS c. o 

-J2 o 

IOIOOSWO rt X3 

t^ r~ t^ o: to g +3 

.§1 

oococo o £ Si 

UO "O* 'Tic'tC en +J 

C) CO C). CO CO ^ o3 

. a is 

lO »C c. i.O uo t^'^ 

r~ i^ t^ i^ t— S; a 

cocococo co 3 3 

"O 

SI 

O000t^-*r-l "5 o 

r-^t^t^oo m 3 

OS OS OS os os g '7* 

. ts^ 

Tf TT CO 00 CN fl M 
^ 3 

CO CO CO CO CO CD -4-a 

CO CO CO CO CO 03 cc3 

CO fc-, 

^03 
m ft 

^ "* '^ O -H ^ J^ 

oi oi oi co cs p,a> 



OO-HCO o 



- -_ 

a-g 

O-w . 

as £ P. 

6t03 

a k§ 

£•& .9-83 
5 S a » 

3 C 3 to 

"O p t 55 

_^ as cS as 
53-3 _*""• 



oOoooooOoo c.2 "33-5 



COCOOSt^iO 

OS OS 00 os os 



El &ll? 



p c3 



fS^o 



P.3 43 

2«= 



Sfi 



be 

q 



6£5J o 3 
343 " 55 

Slit 

. O 3 b 



rHCO CO 



a> s 
fc S 

J -2 



eo co ■* m to 



^ 3'R o 

322§- 

1 c i t <- s a 

c ** cw _c - a 
■a ^ b-- - 1 3 

c ." 1-^.^3 Co 

u g 2 O CD 49 a, 

i.e-?t:= to 
o.c~ > cs 3 — 
feE- °0^-^ 

4* H 



50 



BULLETIN 80, U. S. DEPARTMENT OF AGEICULTURE. 



3 



■(siseq .Wip-anoq) 
sdtqo jo punod jocI 
uoi^suepuoo :]uo.nxIdy 



£ Pift 



•qoin 
9Jt:nbs j.kI U|ni JOJS93 
-tp it; o.iu! 



■v.i.mttuad 
-moj Sninooo amanxsjj 



■qain o.rcnbs -iod g.ms 
-saia oStVBa urnunxxijv 



.2.2 



•ajnssajd 

a3nr:8uinunxmuiy 



■9jns 
-s8jdaSmiSo.ioz;v 



•p3}0£ 



«ob 



las a 

o 



• ^n unox 



-S C. C; r ~ Z. f NNH o 

s •••-•■ • —g j 

-0 M 2 22 22 223 rt 
~ S3 «S 

l, t, I- OCiO I- 1- t~ I_^ 

o MMMKMM CO CO CO. CO 

~oooooo ooo o 

%oo:oooo ooo © 

£ 

BOffiOOOC °°° ° 

►fc oo r-^ 00 00 oo oo odccoo oo 



• £ O0^N 



•HO^N 



■(srseq Xjp-anoq) sdrao 
jo ' punoa jod sjonbn 
■rajsaSip jo oiunioA itfwui 



•X;ionsiwo 



■q^n i^ox 



■SQO^N 



•HO^N 



•sdiqo m J8;ba\. 



•(siscq Xjp-aaoq) 
pagjBqo sdiqo jo ;q3i8A\. 



B° 



^SooiootJ ooocoo 
"2 oi oi oi o> oJ oi 2SS 

.j t~ co -« — i o -r !? "o 12 
^icac*-c- t- 1~ r- 

M " 

OOOOOO SJOtN 
kOOOOOO OOO 

''SiO'O'oio'Oio BEE 

^ CN CN <M <N CN CN CNCNCN 

• *o »o »o «o «o >-o jo £; 2; 
«t-t-i- t-i-i- fcJSS! 

^ CO CO CO CO CO CO CN CO -I* 

e • "• 

-^ co co co co -r co ocoooo 

"y'shNi-N i~ t» E; 

^doooooi os Oi o 

(\ 

!^£ -^ tOIOCfO GC t^ lO 

_o 

*i _ 00 O © © © o CO t^ >-* 
fe rH CO CN CN IN CO M<NCI 

_o 

Si .OOOOOO 0~0 

fcoooooo ooo 

^•toOXOCX-COO ~. OS <~ 

o 

t^noosn") tNtNCT 
(^SoioJos'oooioi ooodoo 



959SS! 

: o o o o o o 

J 5f *r 5" t ■* 8 



CO TO CO 



CO •-< t~ COUO ' 



© p, p_ e< p, ;z, p, APiPi 



•ox jiooj 



t~ 00 Ol O -* tN CO"*"0 



00 



a; Cl 

^ § 

m • ° 

cw 5? CO 

o^ M 

.2^»- 
^§ 

i^a 
.>-2-a 

btK S3 
« C—^J 

m'o a ? 

«— s 

to'2'o 2 
ffi,S « — 

oisf 

25 | § 



§§■8 8 

^p.2, 

° S's 

'y; — C3 > 

"■ — .9 ° 

^030 

— * sr 



PRODUCING SODA PULP FROM ASPEN. 
Table 11. — Yields of experimental pulps. 



51 





Cook 
No. 


Yields 


(bone-dry basis). 


Yields of 

un- 
bleached 

pulp 

(bone- 
dry kisis) 
per solid 

cord. 


Yields of 
bleached 

pulp 
(air-dry 

basis) 
per solid 

cord. 


Kind of test. 


Total 
crude 
pulp. 


Screen- 
ings. 


Screened 

un- 
bleached 

pulp. 


Preliminary 


1 
2 
3 

4 
5 
6 
7 
8 
9 

10 
'11 
12 
13 
14 
15 
16 

17 
18 
19 
20 
21 
22 

23 
24 
25 
26 


Per cent. 
48.01 
SO. 34 
49.31 

46.48 
50.01 
44.67 
52.63 
55. 57 
58.30 

50.36 


Per cent. 

0.05 

.03 

.02 

.01 
.01 
.01 
.03 
.01 
13.02 

.08 


Per cent. 
47.96 
50.31 
49.29 

46.47 
50.00 
44.66 
52.60 
55.56 
45.28 

50.28 


Pounds. 
1,279 
1,342 
1,314 

1,240 
1,334 
1,191 
1,402 
1,482 
1,208 

1,341 


Pounds. 




1,475 
1,444 

1 372 


Group II 


1,467 
1,308 
1,533 
1,625 
1,315 

1 487 






Group III 


51.72 
52.49 
53.70 
55.58 
58.12 

48.67 
50.02 
52.55 
54.97 
54.85 
57.88 

49.18 
51. 61 
50.78 
53.58 


.04 
.05 
.09 
.44 
19.00 

.01 
.02 
.04 
.02 
.09 
.13 

.02 
.01 
.01 
.03 


51. 68 
52.44 
53.61 
55.14 
39.12 

48.66 
50.00 
52.51 
54.95 
54. 76 
57.75 

49.16 
51.60 
50.77 
53.55 


1,378 
1,400 
1,429 
1,471 
1,043 

1,298 
1,335 
fr,400 
1,465 
1,460 
1,541 

1,311 

1,376 
1,354 
1,429 


1,524 
1,524 
1,558 
1,586 
1,109 

1 422 


Group IV 


1,461 
1,530 
1,612 
1,595 
1,666 

1 432 




1,521 
1,483 
1,573 



1 Cook spoiled, due to defect in apparatus. 



52 



BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 



a, 












.usco^ cook- 




<£ 




- y 




c?^ o -£> -f n 


r - 


f -T 


- 


- 






ill 


*-OHH f OHiO-f ffl O 


• SoocdiC". 


•r io o h co ® i-- io -*♦ os 




^HHr- 


,H p-4 tH vH r- 




• ' <N — < c4 ■» — ' -^ — ' -<' -i <?. 


H *I-5 




t» 














h3^ 


^ 














43 -o 

§ £.3 


•*J©o»o OOiOOOO c 


■ oomoo OOOOOO iraO>CO 




§ooodt- 


cD t ~ l ^ OS -*■ OS OC 


'Oodfflri I^ ex' oi c — ' oi CC CR oi -h 




u 


»-H CS 




■ -H r^ r-^ C\ 










K 














3 a 


fti 














43 


•^ O CM 00 ONNCt* « 


"JttOO(DM «DOOX«tO »0(0-* 


•C i 


SCCOO •* -1" O -* -* -q 


Cv 


■ CNrt Cft — O CC-J 


(-0*01 




u 














If 




h. 












— 1 


w 


£ 












co & 

£ & 

MO 

£43 

>02 
















ad 


. os-«#i>- aooooinr-ir 

GsOSOSOO tOI-f i* -fOli 


v 


• Oi IO CS CN 00 irjIOrHiOXa NWMC1 


a 


■ !OOffi«r> 


co *r t- os «o -.c «o os cd ** 


^GClOO OCCNOHr- 

"£ ^ CS CO co co" <n co co c 




t i-H i- 00 -f »o M N Oi -H c; c 

< co oJ cm re cm ec co co co cm c 


1- O CO co 
CM - CO CM* CM 


«t? 


* 












g 


x^, 


^. CC l> 00 M iO C C! iQ C 


■^ 


Ir^CftOO'*'!' ^>r-<0CtO«OCO ONOffi 


&C§43 4<S to 
W ft 




OOh coot> 


a 


'OiO-O-^CO CMCMCCCO-HOO -HCOCOCO 


3 

>> 

42 

5^ 


i-J w cs cm' co" <r 


CS 


' CM CM CM CM CN 


CO CO* C4 <N oi CV 


CO CM CM CM 


— 3 


fc .t-NC 


r-l OS OS cD OS C" 


cr 


• cr cm eft co o o r~ o co oo tc 


CM CM 00 1— 


5 m 

O 


C^CtECCM CO e 
^ «0 


ddci^wV 


S5 


• cSt^i^ioo ^'cii^^NC 


co ■* -r in 

CO CM CM Ci 




CN CS (N CN CO P" 


•CO CM CM CM cr 


COCO CN <N CM C^ 


a; 




CO 
















. 00 CO ce 


'tNCDCOOO^ 


Cs 


! -^ io ti* iocs 


lOtMCO^CDOO t^CN00O5 


S£ 




»o o c 


OOOOOC 


C 


•OOOOO OOOOOO oooo 


C3 


a»-^ wi 














> 


«On 


«ooc 


OOOOOC 


c 


• ooo oc 


ooo OOC 


oooo 


w5« 


3 d ' 














>-.— >> 


■k-'Oi-h OC 


icHOuj'i't: 

OS OS 00 00 00 1^ 


IT 


■OCONHtI 


tJ» -^ 00 i>. 00 i>- CO i-H OS t}< 




a oi • 


gwccc 




•XOt>r-C 


t- I- t^ Os t- O 


oooot-o 




S'al 








' ■ rH ' ' 1- 








« 2 a ft 


K 

£ 






























° A ^ ft 


*<* cc»- 


ooo>ocooc 


kT 


• i-tir)CHOC> 


-^ 00 »m CN -ft t- 


O OCftCM 






—•OC 




|^HH*C 


^H CO iC CN 


*-i 00 


_> 




»OCT 




coo 






a 


60 




















r^cs cc 


(O iO W Ol O) c 
00 00 OS 00 OS CO 


cr 


incOHOu" 


■^ ^ W H '£ C 

o> os oo o> oo a 


fHirJCfiCft 
OO 00 00 00 






"A) 


OOOOOC 


a 


• Oi O0 00 0C O" 






03 8 

^3 
















si 

c 
















03 
















09 


*-(•«** O* 


co cn o i— 1 1*~ r- 


CO 


:__ ^. -*o 


CS CO CO CO CO C" 


CO CM OO 






<2 2-° 


COCO CO 


CO CO CO CO CN i— 




• CO CO CO CO <M 


CO CO CO CO 




_o 


j>1a 


4< « ^ co o d 1 


2 


leiJScoci 


O) — * CD « 4- O 


CO 4" CO CO 

CO CO CO CO 




"o 

O 


MMK 


CO CO CO M CO ^ 


M 


•CO CO CO CO c 


CO CO COCO co c- 




w Eca 
a 


5" ■* •« 


jii^^sj 


J 


• ac co -r -r o 

• CO ^ ^t 4 ^ "1 


iocOOCMi 


ii^ 






■* ■* 1< -3> M IN 


t 


COCO'V't*^*? 




o 

ft 
























































"3 
























































a 


























































tJ 






















































■a 
























































|H 


o 






















































'■< 


























































3 


d 
















c 


: d 








d 






d 


d 










ta 


•s 
















i 


:* 








fee 






is 


■? 










fc 


o 
















c 


• o 








o 






o 


o 


























l- 


• fc- 








s 






h 


u 












42 












a 


ifi 


:^ 






- 


42 




d^c 


4= 












a 












E 


:a 






& 


a 




s a is 


a 
























o 


s 


• 03 






c 


3 




OCSC 


9 












3 












t-t 


S 


. a> 








8 


















|H 












£1 


i- 














42 t- 42 


s 












"oc 

43 " 


o d eo'dP 




■ ,3 o o o e 


« ** w . a A a 


5 d d d 






60 












05 C 


6 


3 > tX 






a 


bo 




a/ bc& 


CuO 
























t- fi 






























3 












Bis 


3 


:3 






c 


3 




OrJw 


3 










q o 


-HtN cr 


-*iO<Ot^0C GT 


C 


^ C4 CO "* iO CC 


1^. 00 Ol Q ~-l CM 


co ^*" W5 CO 
CM CM CM CM 




<S Z 








» 








■ 






















3 


>. 




















o 


co 

c 










h- < 


> 




"S 


1 


a. 


B 


H 


o, 


ft 




a 










3 


a 




n 


"* 


5 


C 




o 


o 




M 




1m 


E 














£ 






c 












e 












a 












o 











PRODUCING SODA PULP FROM ASPEN. 
Table 13. — Caustic soda consumed during cooking. 



53 











NaOH 


NaOH 










consumed 


consumed 






Causl [oil v 


Efficiency 


per 100 


per 100 


Kind of test. 


No 


of black 


in the use 


pounds of 


pounds of 






liquors. 


ofNaOH. 


wood 
(bone-dry 


unbleached 
pulp (bone- 










basis;. 


dry basis;. 






I'i r cent. 


I'i r r, ill. 


Pounds. 




Preliminary 


1 
2 












13.4 


86. 2 


23.1 


45.9 




3 


2.2 


97. 8 


26.2 


53.2 


Group I 


4 


22.3 


77 




65.9 

54.6 




5 


21.4 


77.9 


27. 3 




G 


14.3 


85.3 


25.6 


57.4 




i 


15.3 


S4.2 


18.9 


36.0 




8 


17.2 


82. 1 


16. 1 


29.5 




9 


2.8 


97.1 


14.6 


32.3 


Group II 


10 


4.7 


95 


23.7 


47.1 




'11 
12 








4.0 


95. 4 


23.9 


46.2 




13 


3.4 


96. 5 


24.1 


46.0 




14 


10.2 


89.6 


22.3 


41.6 




15 


18.0 


80.7 


20.3 


36.8 




16 


25.5 


74.0 


18.5 


47.3 


Group III 


17 




94 2 




48.4 
47.6 




IS 


4.7 


95.2 


23.8 




19. 


14.4 


85.2 


21.3 


40.6 




20 


20.1 


79.3 


19. S 


30.1 




21 


27.1 


72.1 


18.0 


32.9 




22 


26.0 


73.2 


18.3 


31.7 


Group IV 


23 


19 4 


80 2 


20 1 


40.9 
39.5 




24 


18.1 


81.5 


20.4 




25 


17.8 


81.8 


20.5 


40.4 




26 


10.3 


89.5 


22.4 


41.9 



1 Cook spoiled, due to defect in apparatus. 

Table 14. — Wood, soda ash. and bleach employed per 2,000-pound ton of air-dry pulp 
(10 per cent moisture) based on experimental results. 





Cook 
No. 


Unbleached pulp. 


Bleached pulp. 


Kind of test. 




Soda ash 




Soda ash 


Bleaching 
powder 






Wood. 


(5S per 

cent 

Na 2 0). 


Wood. 


(58 per 

cent 
Na 2 0). 


(35 per 

cent 

available 












chlorine). 






Solid 




Solid 










cords. 


Pounds. 


cords. 


Pounds. 


Pounds. 




1 
2 


1.41 
1.34 


1,853 
1,308 


1.42 
1.36 


1,872 

1,322 






145.6 




3 


1.37 


1,367 


1.3S 


1,3S4 


136.5 




4 

5 


1.45 
1.35 


2,117 
1 . 738 


1.46 

1.36 


2,126 
1,757 


108 4 




127.4 




6 


1.51 


1,661 


1.52 


1,681 


136.5 


• 


7 


1.28 


1,057 


1.30 


1,074 


164.0 




8 


1.22 


901 


1.23 


912 


255.0 




9 


1.49 


828 


1.52 


844 


532.5 




10 

211 

12 


1.34 


• 1,259 


1.34 


1,259 


141 3 








1.31 


1,191 


1.31 


1,196 


181.2 




13 


1.28 


1,172 


1.31 


1,196 


174.7 




14 


1.26 


1,11."> 


1.28 


1,167 


192.7 




15 


1.22 


1,177 


1.26 


1,211 


27S. 1 




16 


1.72 


1,571 


1.80 


1,612 


432.3 


Group III 


17 

IS 


1.38 
1.35 


1,258 
1,235 


1.41 
1.37 


1,276 
1,254 


127.8 




140.2 


1 


19 


1.28 


1,178 


1.31 


1,196 


104.7 




20 


1.22 


1,126 


1.24 


1,137 


182.1 




21 


1.23 


1, (28 


1.25 


1,148 


201.2 




22 


1.17 


1,071 


1.20 


1,101 


351.2 


Group IV 


23 
24 


1.38 
1.31 


1,254 
1,191 


1.39 

1.32 


1,270 

1.1 '.i'i 


155.7 




162.9 




25 


1.33 


1,214 


1.35 


1,232 


173.5 




26 


1.26 


1,149 


1.28 


1.16(1 


200. o 



> Cook spoiled, due to detect in apparatus. 



54 BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 

METHODS FOR AUXILIARY TESTS. 

In determining bone-dry weights, properties of pulps, and concentrations of soda 
liquors, the following methods were employed: 

BONE-DRY WEIGHTS. 

In practically all determinations involving exact quantities of wood, pulp, or 
screenings, either actual or calculated bone-dry weights were used. The actual 
bone-dry weight is the weight of the material after having been dried to constant 
weight in an oven with good circulation of pure air at a temperature of 104-100° C. 1 
Usually instead of drying the entire quantity of material, its "bone-dry factor," or 
the ratio of the bone-dry weight to the weight before drying, was determined by 
means of a small sample. The calculated bone-dry weight is the weight obtained 
by use of this factor. The errors in calculated bone-dry weights were found by actual 
test to be less than 0.3 per cent. 

PROPERTIES OF UNBLEACHED PULP. 

Color. — The color of a pulp was determined by visual observation and also by 
means of an Ives new construction tint photometer. The standard for comparison 
was a block of magnesium carbonate, which affords photometer readings of 100 each 
for the red, green, and blue color screens used. The sum of the three readings for 
a pulp measures its "whiteness," and this sum subtracted from 300 2 (the sum of the 
three readings for a surface as white as the standard) measures the "parts black" rat- 
ing of the pulp. The higher the "parts black" value the darker is the pulp. This 
method of expressing relative "darkness" of different pulps is reliable only when 
the pulps are of approximately the same hue, as in the case of these experiments. 

Shivcs. — Shives in pulp are the small bundles of wood fibers which were not reduced 
by the cooking and subsequent operations, and which were not removed by the pulp 
screens. For the determination, a three-tenths-gram portion of pulp, the bone-dry 
factor of which was known, was thoroughly broken up in a small Erlenmeyer flask 
and deposited on a 70-mesh sieve in an even deposit or sheet covering 9.66 square 
inches. This sheet was "couched" on a silk cloth and then transferred to a glass 
plate and dried in an oven. When the plate with the deposit was placed in front of 
an incandescent lamp the shives could easily be counted with the eye. In cases 
where the number was large, a glass plate divided into quarter-inch squares was 
placed on top of the pulp and a small area was examined instead of the whole. Know- 
ing the area examined and the bone-dry weight of the pulp sheet, the number of 
shives per gram of bone-dry pulp could be calculated. 

Ash. — The ash was determined by burning a bone-dry sample of unbleached pulp 
of known weight in a platinum or porcelain dish over a Bunsen flame until the ash 
produced was free from carbon and of a white or grayish-white color. The percentage 
of ash is based on the bone-dry weight of the pulp. 

Strength. — The strength of the pulp sheets made on the paper machine was deter- 
mined by a Mullen paper tester and by a Schopper breaking-length testing instrument. 
The pulp was tested in the ordinary air-dry state for the conditions that prevailed 
in the laboratory. The Mullen test, or "pop test" as it is sometimes called, was 
made by clamping a single sheet, accurately measured for thickness, between a rubber 
diaphragm and a polished metal ring, and then, by means of liquid under pressure, 
forcing the diaphragm against the pulp sheet until it burst through the aperture. 
The pressure on the liquid in pounds per square inch, or "points," is read from a 



i The weight was considered constant when the decrease was not more than 0.1 per cent during an addi- 
tional hour's drying at this temperature. 

2 At the time of these experiments the shutter of the instrument used had been injured and could not 
be opened more than 64.7 points. The other aperture was then reduced to this size and the value 04.7 
was use 1 in place of 100 for a wide-open aperture, and 194 (3 times 64.7) was used in place of 300. The results 
obtained for the various pulps were sufficiently accurate for comparison with each other. 



PRODUCING SODA PULP FROM ASPEN. 55 

gauge. For each pulp 20 sheets whose thickness varied between 0.010 and 0.011 inch 
were tested. The average strength in pounds per square inch per 0.001 inch thickness 
is the quotient of the average test value divided by the average thickness in thou- 
sandths of an inch. A quantity one-tenth of this value is sometimes used in express- 
ing results, and is called the "strength ratio." ' The Schopper tester measures in 
kilograms weight the tensile stress required to break a strip of pulp 15 mm. wide. At 
the same time the instrument registers the "per cent stretch," which is the strain or 
elongation of the strip just before breaking, and is expressed as a percentage of the 
original length. The "breaking length" is the length of sheet which, if suspended, 
would break of its own weight, and when expressed in meters is determined by multi- 
plying the weight in kilograms required to break the strip by its testing length in milli- 
meters (180 mm.), and dividing the product by the weight in grams of the portion 
of the strip subjected to test. Five strips of pulp were tested in the "machine 
direction" of the sheet and five across the machine direction, and the average 
values for the two directions determined. 

Bleach required. — The bleaching solution was made by mixing bleaching powder 
(calcium oxy-chloride or chloride of lime) with water and allowing the mixture to 
settle so that a clear solution was obtained. The strength of this solution was deter- 
mined by titrating 5.00 cc. against fifth normal arsenious acid solution, using a solu- 
tion of starch paste and potassium iodide as indicator. The number of cubic centi- 
meters of arsenious acid used, multiplied by 4.0514, gave the strength of the bleaching 
solution in grains per liter of "35 per cent bleach," or bleaching powder, in which 35. 
per cent of its weight is chlorine available for bleaching purposes. The bone-dry 
weight (about 50 grams) of the pulp sample used for the bleaching determination was 
first calculated by means of its bone-dry factor. The sample was then thoroughly 
broken up in water 2 to form a uniform pulp mixture. A quantity of the bleaching 
solution containing a known weight of "35 per cent bleach " was added and the mix- 
ture diluted with water 2 to approximately 2,500 cc. This mixture was kept at a 
temperature of 40° C. until the bleach was exhausted, as determined by starch -iodide 
indicator. The bleached fiber was then thoroughly washed free from bleach residues 
and made up into sheets on a small hand mold. These sheets, when air-dry, were 
compared with air-dry standard color sheets made in a similar manner from five or six 
commercially bleached soda pulps mixed in equal proportions. If the first determi- 
nation on the experimental pulp did not give as white a color as the standard, the 
process was repeated on other samples until the standard color was attained as nearly 
as possible. 3 The weight of 35 per cent bleach required to produce the standard 
color is expressed as a percentage of the bone-dry weight of the pulp. The bleaching 
operations were performed in enameled jars provided with agitators and placed in a 
tank of water whose temperature could be regulated by an electric heater. It was 
found best to start the bleaching in the late afternoon or evening, so that the bleach 
was exhausted sometime the next morning. The comparisons with the standard 
color sheets should be made at about the same time each day, using light from a north 
window. 

Loss on bleaching. — For determining the loss on bleaching, a sample of about 2 
grams of pulp was thoroughly broken up in water and bleached in a 250 cc. Erlen- 
meyer flask, using as near as possible the conditions which, produced the standard 

i "Strength factor" or "points per pound" is distinguished from "strength ratio" by the former being 
obtained by dividing the "pop test" by the weight in pounds of a ream of paper. The size of a ream varies, 
but for a standard of comparison a ream of 500 sheets, 24 by 36 inches, is usually preferred for determining 
the strength factor. 

2 The water should be neutral so far as its action on pulp and on bleaching powder solution is concerned. 
The use of distilled water is preferable. 

3 Actual tests have shown that this method gives results almost identical to those secured in pulp-mill 
operations. The method of determining the amount of bleach required by adding an excess of bleaching 
powder and titrating the unconsumed excess after the pulp is bleached sufficiently while, gives much 
lower results. 



56 BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 

color in the samples tested for the determination of the amount of bleach required. 
The bleached sample was thoroughly washed, first with hot distilled water and after- 
wards with ethyl alcohol. Its bone-dry weight was then determined. The per- 
centage loss on bleaching is based on the bone-dry weight of the unbleached pulp, 
which had been calculated from its bone-dry factor. 

Microscopic examinations. — Representative portions from the pulp sheets were 
soaked in water, teased apart with a needle, stained with Bismarck brown, dehydrated 
with absolute ethyl alcohol, cleared in xylol, and made into permanent mounts with 
( 'a inula ba Isam. Photomicrographs of these mounts magnified G5 diameters were used 
in studying the individual fiber characteristics. Further microscopic study of each 
of the individual mounts was also made, using different magnifications, and such 
features were observed as the apparent strength of cell walls, the prominence of cell 
markings and the presence of vessels, fiber bundles (shives), and ray cells. The 
general shape and condition of the fibers and the distinguishing characteristics for 
the species were noted. By means of a micrometer eyepiece about 50 unbroken 
fibers from the various mounts were measured for length and breadth at the middle 
of the fibers, and the average thickness of the cell walls was roughly estimated. The 
fibers were selected at random, no effort being made to select extremely long or short 
ones. 

ANALYSES OF SODA LIQUORS. 

The caustic-soda solutions charged and the black liquors from the leached pulps 
•were examined for their contents of cooking chemicals, in the first case to calculate 
sizes of charges, and in the second to determine the consumption of caustic soda during 
cooking. 

Caustic soda liquor. — The examination of the caustic soda liquor was conducted as 
follows: A 10 cc. portion was titrated against normal sulphuric acid, using phe- 
nolphthalein as first indicator and methyl orange indicator to finish the titration. 
Letting Y=the number of cubic centimeters of normal acid solution required for 
the first end point and X=the number of cubic centimeters required for the final 
end point, the following equations were used for calculating the concentration of 
caustic soda (NaOH) and the causticity: 

4 (Y-(X-Y))=grams per liter of NaOH. 

IOO(Y-iX-Y)) 

y i= per cent causticity. 

Black liquor. — The examination of black liquor w T as conducted as follows: 

(1) A 50 cc. portion of black liquor was evaporated to dryness in a platinum dish. 
The residue was ashed over a Bunsen burner and the soluble salts were leached out 
with hot distilled water. The entire solution obtained was titrated with normal sul- 
phuric acid, using methyl orange as indicator. The number of cubic centimeters of 
acid required to produce the end point multiplied by 0.62 gives the grams per liter 
of total sodium oxide (Na^O) in the black liquor. 

(2) A 100 cc. portion of the same black liquor was mixed with 50 cc. of 10 per cent 
barium chloride solution in a 500 cc. calibrated flask. The mixture was then diluted 
to 500 cc. with neutralized or freshly distilled water free from carbon dioxide and 
thoroughly agitated. After settling, 50 cc. of the clear supernatant liquor were titrated 
with tenth normal hydrochloric acid, using phenolphthalein as indicator. The num- 
ber of cubic centimeters of acid required for the end point multiplied by 0.401 gives 
the number of grams per liter of free caustic soda (NaOH) in the black liquor. 

(3) The causticity of the black liquor was calculated from the following equation: 

A (0.775) 100 

— * — ^-^ =per cent causticity. 

In which: 

A = the number of grams per liter concentration of caustic soda (NaOH). 

B=the number of grams per liter concentration of total sodium oxide (Na^O). 



PRODUCING SODA PULP FROM ASPEN. 



57 



AUTOCLAVE TESTS ON ASPEN. 

A few autoclave tests on aspen (Populus tremuloides Michx.) were made in 1909. J 
The ordinary soda process was employed, but the digester used was a horizontal, rotary 
autoclave, made of 6-inch steel pipe, with a capacity of about 2 gallons. As the heat 
was furnished by Bunsen burners, there was no condensation or loss of liquid through 
overflow to modify the cooking conditions. Cooks were not blown, but the digester 
was quickly cooled to room temperature and then dumped. The pulps were thor- 
oughly washed with cold water and screened on a small diaphragm screen through 
slots of 0.006 inch width. The test material was cut from fairly young growth near 
Ridgeway, Colo. Portions of the logs tested, especially the centers and around knots, 
were discolored a dull reddish-brown, probably due to incipient fungous attack; other- 
wise the wood seemed to be sound. Chips were prepared in the manner described on 
page 15. Their sizes were five-eighths inch (with the grain) by three-sixteenths to 
one-fourth inch by one-half inch to 6 inches (both across the grain). 

The data resulting from the tests are shown in Table 15. The column headings 
have the same significance as those in Tables 10 to 14, except as otherwise indicated. 
However, in the bleaching tests the standard color matched was that of bleached 
sulphite pulp, and, as soda poplar pulp in commercial operations is never bleached 
to so white a color, the test data should be reduced somewhat in estimating the com- 
mercial value for bleach required. The values for loss on bleaching also are probably 
a little greater on this account. 

The tests fall naturally into two groups. One of these consists of cooks 1, 2, and 4, 
in which the concentration of caustic soda in the cooking liquors was varied. The 
other consists of cooks 3 and 5, in which the duration at maximum pressure was the 
chief variable. Increases either of concentration or of duration resulted in decreases 
in the yield of pulp, loss on bleaching, and bleach required, except possibly in the 
case of one cook. All of the pulps produced were thoroughly cooked. The yields, as 
compared with those secured in the more recent tests (see Table 11), were uniformly 
very low and the losses on bleaching very high. The difference may be due to the 
methods and apparatus used or to deterioration of the wood from fungous attack, or to 
both. If the wood had been perfectly sound, it does not seem probable that the lower 
yields would have been accompanied by the higher amounts of bleach required and 
the larger losses on bleaching, even though these effects were slightly augmented by 
the higher standard of bleaching. 

Table 15. — -Cooking conditions and results of autoclave tests on aspen. 





Date of 
cook. 


Weight 
of chips 
charged 
(bone-dry 
basis). 


Wauer 

in 
chips. 


Liquor charge. 


Initial 

volume of 

digester 

liquors 3 

per 
pound of 

chips 

(bone-dry 

basis). ' 


Chemicals charged per 
100 pounds of chips 
(bone-dry basis). 


Cook 
No. 


Initial concentrations. 8 


Caus- 
ticity. 


NaOH. 


Na 2 C0 3 . 


Total 
Na 2 0. 


NaOH. 


Na 2 C0 3 . 


Total 
Na 2 0. 


1 
2 
3 

4 

5 


1909. 
May 25 
May 27 
June 2 
June 8 
July 3 


Lbs. 
1.652 
1.652 
1.652 
1.304 
1.920 


P. ct. 
33.5 
33.5 
33.5 
IS. 3 
15.0 


Gravis 

per liter. 

80 

so 

90 
SO 
90 


Grams 

per liter. 
7.4 
1.8 
4.3 
1. t 
4.3 


Grams 
per liter. 
C6.3 
39.8 
72.3 
24.1 
72.3 


P.ct. 
93.5 
97.5 
96.5 
96.5 
96.5 


Galls. 

0.375 
.599 
.386 

1.000 
.390 


Lbs. 
25.0 
25.0 
29.0 
25.0 
29.3 


Lbs. 

2.3 

.9 

1.4 
1.2 

1.4 


Lbs. 
20.7 
19.9 
23.3 
20.1 
23.5 



i These tests were made by Mr. Edwin Sutermeister, formerly in charge of the pulp-testing laboratory 
of the Forest Service at Washington, D. C. 
* The water in the chips when charged is not taken into consideration. 



58 BULLETIN SO, U. S. DEPARTMENT OF AGRICULTURE. 

Table L5.- < 'ooling conditions and results of autoclave tests on aspen — Continued. 





I Miration of cooking. 


Maxi- 
mum 
gauge 
pressure 

per 
square 
inch. 


Yields (bone-dry basis). 


Properties of unbleached 
pulps. 1 


Cook 
No. 


Tot ill. 


\i zero 
gauge 

pros- 
sure. 


At 
maxi- 
mum 
gauge 
pres- 
sure. 


Total 
crude 
pulp. 


Screen- 
ings. 


Screened 
pulp. 


Ash. 


Bleach 
required. 


Loss on 
bleach- 
ing. 


1 
2 
3 
4 
5 


Hrs. 

8.2 
8.5 

{■ s 

8.0 
8.0 


Urx. 
0.3 
.3 
.3 
.2 
.3 


Mrs. 

7.0 
7.0 
3.0 
7.0 

7.0 


Lbs. 

no 

110 
110 
110 
110 


P.ct. 

41.10 
44.23 
40.50 
46. 97 
36.00 


P.ct. 

0.10 

.03 

.10 
.07 
.00 


P.ct. 
41.00 

11.2(1 
40.40 
46.90 
36. 00 


P.ct. 
1.40 
1.27 
1.35 
1.25 
1.42 


P.ct. 
15.4 
14.7 
11.3 
15.8 
10.0 


P.ct. 
3.92 
4.08 
4.39 
4.68 
2.56 



(P. L.— 66— 1,S. 683.) 
i The pulps produced were of good strength and of a fair degree of hardness; the color was very light 
reddish-brown. Strives were very few in number or almost absent. 



ture. 



,rt of cook. 



Concentration of 
NaOH. 



G per cent ' 



2 per cent l (?) . 



7 percent 1 . 
7 percent 1 . 



Pel 



6-9 percent 



6-8 percent. .. 
5-10 per cent [ . 



. r > -7 percent NazO. 



7-9 percent 1 . 
5-7 per cent ' . 



45-60 minutes; total perk 



58 BULLETIN 80, r. S. DEPARTMENT OF A.GRICULTUBE. 

Table 15. — Cooking conditions and results of autoclave tests on aspen — Continued. 





Duration of rooking. 


Maxi- 
mum 
gauge 
pressure 

per 
square 
inch. 


Yields (bone-dry basis). 


Properties of unbleached 
pulps. 1 


Cook- 
No. 


Total. 


At zero 
gauge 
pres- 
sure. 


At 
maxi- 
mum 
gauge 
pres- 
sure. 


Total 
crude 
pulp. 


Screen- 
ings. 


Screened 

puli,. 


Ash. 


Bleach 
required. 


Loss on 
bleach- 
ing. 


1 
2 
3 
4 
5 


Hrs. 

8.2 
8.5 
4-6 

8.0 
8.0 


Hrs. 
0.3 
.3 
.3 
.2 
.3 


Hrs. 
7.0 
7.0 
3.0 
7.0 
7.0 


Lb?. 
110 
110 
110 
110 
110 


P.ct. 

41.10 
44.23 
40.50 
46.97 
36.00 


P.ct. 
0.10 
.03 
.10 
.07 
.00 


P.ct. 
41.00 
44.20 
40.40 
46.90 
36.00 


P.ct. 
1.40 
1.27 
1.35 
1.25 
1.42 


P. ct. 
15.4 
14.7 
14.3 
15. S 
10.0 


P. ct. 
3.92 
4.08 
4.39 
4.68 
2.56 



(P. L.— 66— 1,S. 683.) 
i The pulps produced were of good strength and of a fair degree of hardness; the color was very light 
reddish-brown. Shives were very few in number or almost absent. 



J 


















Table 10.— 


Cooking conditions employed in the soda process 


rtf wood- 


mdp mannfaeture. 


















Refer 
ence 
No 


Practice followed. 


Digester. 


Quantity of chemicals charged. 


Quantity of cooking 

liquor charged. 


Cooking Liquors at start of cook. 


Cooking 

per 
square 
inch. 


Cooking 
tempera- 
ture. 


Durations of cooking. 


Blowing 

T-r,- .lire 

per square 
incn. 




Kind. 


Size. 


Wood 


■ 


Actual caustic 

VlOII). 


| ioda 

carl> I] 


'ercook. 


Per cord. 


Density. 


Concentration of 


Caus- 
ticity. 


Total. 


Prom start 
till cooking 
pre iure Is 
reached. 


At 
cooking 
pressure. 


AutftOrlty.' 




Baum& 


Twaddle. Specific gravity. 




1 


Watt and Burgess process 




Feel. 










Gallons. 


12° 


18° ' 1. 09 
(«) 


-i ' - . . 


Pit ctnt. 


Pounds. 

BO 

90 

180-200 

180 

150-180 

05 or 

no 

90-110 
90-110 
100-110 


'F. 


Hours. 


Hours. 


Hours. 


Pounds. 




2 
















m 












10-12 
[).5orless. 




in, 1007. 


3 
















60 per 

cwt. dry 

wood." 












Not blown. 


4 




vertical. 






• 








'0° ' 1. 0J 














i 


European practico (1870) 








per ton 

green wood. 
















300-375 












B 


American practice (1870) 












i 18° 


i 1.08 
' 1.00-1.12 

' i 08 












05 or more. 
45 


nofmann, 1873; Watt, 1907. 


- 


American practice (1880-1890) 


vertical. 




27 by 7 


■ 






;:. 100 






' 18° 

112-21° 

i [6" 
i lS-22° 

(>) 









2;-3 


7 


1889; Watt, 1907. 


s 


do 








12 I4°i ' E 

(•) 








<8-10 






D 


do 


Cylindrical, stationary, 
vertical. 






'■oils, or 
direct lire. 








More 
than 700. 
70(1 




Qrtffln and Little, 1894. 


10 


....do 




















8-10 
6-10 

<•) 




























27 l>y 7 


1 r. e steam 


nl lis. per 
cord. 1 


1,320 lbs. 


1,1 


BOO 
1,100 


10-15* at BO" F. 
(') 


' 11-21° 
(') 


(») 








'8J-13 


2J-3 
(•) 


76 






13 


- .do 




Technology, 1902. 
in, 1907. 
1907. 












His. per 

cord. 


























; cenl of 
nrelghl of wood. 
















130-160 

132-147 

73-147 
ft-178 

100 150 

12.-. 


\ 


<0 

<6 
<5-6 
•5-6 

8-9 








Stevens, 1908, 


















/10' 


i 11° U.07 

i is 1 ' 1.08 

■18-22° 1 1.09-1. 11 

i 15-22° '1.07-1 II 












Schubert; Stevens, 1908. 








































Ernst M tiller; Stevens, 1908, 












::: 




















Klemm; Btevens, 1908. 










■' 1111 






















1908. 
































Beveridge, 1911. 






tancnery. 




do 










211° 1 1. Ill 










g 8 
• 1-2 




Cross, Sevan, and sindall, 








8.5 eu. 

300 CU. 
Chips, 




637 kilos ( = 1,100 
lbs.)' NatO tor 

chiirpe. 




liters 
( = 1 ,321 
galls.)' 














. 




1911. 
Bennefeld; Beveridge, 191L 































■ 
- Strong si-hit ion 
a In addition to tin- i * i 1 1 i .'m- ■ ■ - 1 . i ^ < ■ < H required for charging digester, 30-4fi minutes; for relieving pressure and blowing, (5-60 minutes; total period fur at 

* Not sf'i ■ ■ iu't h. r time is total duration or duration at maximum pressure. 

* i e <■■ in in 12 houi i. 

'See Bibli ' ' ' i nled references. 



31091°- Bull. 80—14, (To face p 



PRODUCING SODA PULP FBOM ASPEN. 



59 









c 


P 


O 


c 


c 










i-O 




C 


O 








a£ O *c 













1- 


-r 


O 


Iff 

O C3 






'bo >c 


ua oc 


05 


CO 








1-- en 


CO 


00 




ft. 


^SP £ 




" 


































a ° 


M 

O 



*! J. P> 1 

2 00 c 


00c 


1 









00 c 


= 







00c 








= = 


?- 





a c 


goooo 10 c 


10 1-1 








re — c 


c 




caS 






















£3 -co 


-co" of co 


-co 










CM 


CO 


H, 1 * 


u 


e CM 0- 




CM 














ffa 


£ 







" 
















p 


•d 































"3 

































CJ 


03 03 
































SO 


•O ° • 
































03 


OJl« 


a. 






























cj 




«0 


T 






























$ 


So e 



























03 
o 


^2 


00 c 

ft, . c 

























a 


P, 


~ l ~ 


'"' 














> 
































fl 


73 
























u 


U 


u 


o 


■o 








a 




CJ 














a 


V 









P 


, 


P 


H 


p. 












P, 1 


o 






V 


























>> 






C 
5 








£ 












C 




•a 


a 

03 
P 


SO 




P 
c 


-> 

•d 


S 1 
3 «> ° 
.00,. 










P "• P a 

Q. S) O .O 


a? 


ca w 




CK 


m 




t. a> 


t, 












™ 


>-■ "O 


3 




c 







if, 


= p.'" 

' — c 














o- 


00 80 








p 




fi 


"a II 
















CJ 




<i 




t> 


CC 


CM II 












CM 


s 


CO 




si 


t, 






























.5 

































03 


sS 


*J 




























~ 


2SE 










a 
















O 


w—« 








S3 
















E-l 


M ai 

© o) a 


























Cy 


03 ^ a 


_o 




M O O 1 


c 


c 




a 

a 








O-O 


■C 


— 


■c 


t: 


- 
































3 


J h= 


xljl 








J 
















CO if 


CO If 


>o 


■ra 


lO CM ■* 


if 







o3 . 


















« t>> 






CO 


■o 


■■O 


CO 






T3.-B 


'g «* 



































O 03 


<3 
















fe P. 


















p " 




















l~ 




P 


r- 


CO C3> CO 0> t^ t> 


r> 


r- 
























• 


^: 








> >, 


!>>>> >. !>>!>. > 


1 > 


^ >. 




S] 


^ 


,c 




£ 




kP^^^.C^ 


£■ 


JP 




s 


ft, 


K 




a 





OOONI-ff 


c 









CN 




■t 


CJ 


CO *i*CO -V CM O 


CN 


CO 


c 


































0) 




































































M 


































05 


































M 




































































5 


























2 


' 








































03 










C3 








"r 










■d 


CJ 






"3 


^3 








c 










p 








a 




















5 


3 

> 

u 

03 
P 










C3 
P 








a 
> 

Q 

c 
c 


' 




































03 








C3 








C" 





















w 












































































03 






C3 


C3 








r 












Zj 






O 


O 








- 














































H 


'b. 




















•0 e 


d c 


-9 


*o O O O O^ 


c 









.5 - 


■a t 


| 


j'O'B'SflC 


" 


•0 
































x 






>. 


t>> 






: > 






















O 






;t 








* i*5 


I 

cr 


OJ ^ 




r^ r^ r^ 1. -r w 

00000c 


c 





^o 


c 


c 





> r- 




OJ 


o> a 


era 


oa cji c3> a> c 


C 


a> 


^ o P. 


tH f- 


»-t r- 


rt 


„ rtrtrtrt j. 


T " 




.god 


_, J, 


CO -1 


10 


»l»»010- 


O 


n 








rl 1- 




rt 


1 C 


u 


l* 

































P, -O 

S -2 

2 p 

B ^ 

'id 5 

- cj . 

- - ^ 

cs^-3 

^ (_ HH 
P « . 

&g<l 
£ o >» 

p" 3 a 

„ c „ 03 



GO 



BULLETIN 80, U. S. DEPARTMENT OF AGRICULTURE. 





































ft'g 

.5 - 

> yj 
O t - 


Oh 


7: 










— CD 




o = ■ 




« p, 




12 X SB 




M 

.E i 

o S 

C x 


o 
si i 


irs o: ac 
© *o *& 










X 


■ i 
»o 00 




S 


3'-' 
















- 2 


m 


00 














hi 


< ~ 


















s % 'Z ■«' 


CO 


XCN .-H 














IOCN 


o 

o 


ot'CN 


1 














oiio 




s 


"O 
















*3 
a 


1 sis 


1 


rt 
















3 




o 


CN O X to 00 00 <C O 


X X<D 


3 
A 




1 1 uj t^tOtO'O 
Oio 


ci >i 




73 


fe o 


Ol 








3* 








o 


l? 30 








H 


<N 03 


















oo-" 








MCC „. 


On'O 


O0»0 OOOOiOOOOO 
HMl. — iOO-hO-hcO — CN 




8 i R 5-.S 


ry CS 










§2 


^ a ^ 




&■** 






o a M 




, 


•«'tN 


tN 


(N 












XO'O 




_o 


Koi 


CT> 


X 












0,0,0 




a >, 


v> 


oo 


















3.-H 


^ 


00 














ea 




S3 






















o 


&< 


























Ui 
























c 

o 






Ph 




















































































W) 






-^ 
























l-i 






























es 






























P. 






_, 






















W 

o 


.P 






p 






















03 


03 


























o 


'A 


O 






T3 
















































o 


o 


•a 






o 






















a 


c 






P. 




















o 


.2 


3 
O 






to 




















£j 


a 


P. 






o 




















co 




£ 




- 


o C 








q 

03 








03 


a 
c 
o 


■w 












Z« 










a 


a ° » ■ <E 








W -fcJ +^ -M 


o 


o 


0J 








cfliia 


1 3 




73 










cd cu a> a> 














ocisti 














u, u. t~> u 






3 


mo 3 o3 i 








CD CD CD CD 


bo 

.S 




a 1 


p,^ cr&c»o 








PPPP. 




W 


oiJjW oo 








COMOCOJ 


o 


















o 






C3 


HMiO HMKOlOtSCOiCJCl 
HHO .-HrHrtOOOOOO 








o 






p l 

GO M 


1 

8 


« 1 a J. 1 I s - - 






rH 


PH IH iH t-i IH 












&►. 







ooo ooooooooo 






00 


CN ^r O <N "X: :C OO SO "f X 0C X 






"3 

■a 




CNCNH WMNrtH . f-h »-H pH 




1 


1 


-•J-" © CN CN 1~ "" rf "" 




o> 


■a 




»-< CNNCMH 




Q 


03 

is 








Q 


ooo ooooooooo 










TtO'O •^rcOCOCNiO'-'CNCNCN 






•^' 










i 


ti 


IN 1 1 1 1 O 1 

© 0O -T- -r — i ^ io 






3 










03 










« 








, 


^ 


<N CO ■*»* tocOI^&OOiO^IMCO 




!r <D • 








A 3 o 







































m.tl 


1* 


T3 03 





o . 


3 


B^ 


>» 






•Bifi 


o 




a 


-M CD 


a s< 


3 CD 


" 






"ea d 






1^ 


O03 



PRODUCING SODA PULP FROM ASPEN. 61 

BIBLIOGRAPHY. 

(January, 1913.) 

PROPERTIES OF ASPEN AND ITS USE AS A PULPWOOD. 

Journal of the Society op Chemical Industry. Poplar wood pulp. In: Jr. 
Soc. Chem. Ind., 24 (1905), 148. 

LTndustria della Carta. Poplar and the paper industry. Extract in: Paper 
F(1911), (5), 13. 

Litchauer, Viktor. Die " amerikanische Aspenzellulose." 3 pp., illus. In: 
Zentrallblatt fur die oster.-ungar. Papierindustrie. XXIII (1905), (26), 822-5. 

Macmillan, H. R. Forest products of Canada: pulpwood. Bulletins 12 (1908); 
26 (1910); 30 (1911), Forestry Branch, Department of Interior, Canada. 9; 14; 17 
pp., tables, 8°. Ottawa; Government Printing Bureau, 1909; 1911; 1912. 

Papier Fabrikant. Die Pappel (Populus canadensis) als Papierholz. In: Papier 
Fabrikant, 9 (1911), 199-201. 

Sargent, Charles Sprague. Report on the forests of North America. Vol. IX, 
Reports of the Tenth Census, United States Department of the Interior, Census Office. 
612 pp., maps, tables, 4°. Washington: Government Printing Office, 1884. 

Svensk: Pappers-Tidning. Poplar as a pulpwood in Italy. Swedish translation 
of an Italian letter. In: Svensk Pappers-Tidning, 12:te arg. (1909), (22), 225-6. 

United States — Agriculture, Department of — Forest Service — Bulletins 
74 and 77. Forests products of the United States, 1905; 1906. Wood used for pulp; 
pulpwood consumption. 6; 8 pp., tables, 8°. Washington: Government Printing 
Office, 1907; 1908. 

United States — Commerce and Labor, Department of — Census, Bureau of — 
Forest Products No. 1. Pulpwood consumption: 1907; 1908; 1909; 1910. 14; 12; 
15; 10 pp., tables, 8°. Washington: Government Printing Office, 1908; 1909; 1911; 
1912. 

United States — Commerce and Labor, Department of — Census, Bureau of. 
Paper and wood pulp statistics; preliminary report for 1909. 6 pp. , tables, 8°. Wash- 
ington, April 26, 1911. 

Weigle (W. G.) and Frothingham (E. H.). The aspens: their growth and man- 
agement. United States Department of Agriculture, Forest Service, Bulletin 93. 35 
pp., tables, 8°. Washington: Government Printing Office, 1911. 

THE SODA PROCESS OF PULP MAKING. 

Bersch, Joseph. Cellulose, Cellulose-produkte und Kautschuksurrogate. Berlin, 
1903. English translation, "Cellulose, cellulose products and artificial rubber" by 
Wm. T. Braunt. 336 pp., illus., 8°. Philadelphia: H. C. Baird and Co., 1904. 

Beveridge, James. Papermaker's pocketbook. 2d ed., 225 pp., illus., tables, 8°. 
London: McCorquodale and Co., Ltd., 1911. 

Clapperton, George. Practical papermaking. 2d ed., 226 pp., illus., 8°. 
London: Croxby, Lockwood and Son, 1907. 

Congdon, E. A. The manufacture of chemical fiber. In: School of Mines Quar- 
terly, X (1889)! 163-172. 

Cross (C. F.) and Bevan (E. J.). Textbook of papermaking. 2d ed., 330 pp., 
illus., tables, 8°. London: E. & F. N. Spon, Ltd., 1900. 

Cross (C. F.), Bevan (E. J.), and Sindall (R. W.). Woodpulp and its uses. 270 
pp., illus., 8°. New York: D. Van Nostrand Co., 1911. 



62 BULLETIN 80, U. 6. DEPARTMENT OP AGRICULTURE. 

De Cew, Judson A. The function of the caustic soda process in the production of 
cellulose from woods. In: Jr. Soc. Chem. [nd., 26 (1907), 561-3; Chemical Abstracts, 
1908, 319. 

Griffin (R. B.) and Little (A. D.). The chemistry of papermaking. 515 pp., 

illus., 8°. New York: Howard Lockwood and Co., 1894. 

Hofman, Karl. Praktisches Eandbuch der Papier fabrikation. 2d ed., 2 vols., 
1800 pp., 4°. Berlin: Papier Zeitung, 1897. 

International Library of Technology, Vol. 20, Taut 2. Manufacture of paper. 
58 pp., illus., tables, 8°. Scranton, Pa.: International Textbook Co., 1902. 

Klein, Arthur. The process of manufacturing chemical wood pulp. Proceed- 
ings, Verein der Zellstoff- und Papier- Chemiker, Berlin, 1909. Also in: Papier Zei- 
tung, 84, 227, 267: Chemical Abstracts, 1909, 1341. 

Leighton, Marshall Ora. Preliminary report on the pollution of Lake Cham- 
plain. United States Department of the Interior, Geological Survey, Water Supply 
and Irrigation Paper No. 121. 119 pp., illus., 8°. Washington: Government Printing 
Office, 1905. 

Paine, Jr., A. G. Description of the soda process as practiced at the mills of the 
New York and Pennsylvania Company, 1908. In: Vol. IV (pp. 2628-2633) of Pulp 
and Paper Investigation Hearings. United States House of Representatives, 60th 
Congress, 2d sess., Doc. 1502. Washington: Government Printing Office, 1909. 

Reid, T. Anderson. Wood as a papermaking material. Tables. In: Jour. Soc. 
Chem. Ind., 5 (1886), 273-276. 

Silcox, George W. Report on the art of printing and on manufactures of paper. 
With appendix, 30 pp., index, 8°. In: Vol. II, Reports of the Commissioners of the 
United States to the International Exhibition held at Vienna, 1873. United States 
Department of State. Washington: Government Printing Office, 1875. 

Sindall, R. W. The manufacture of paper. 275 pp., illus., bibl., 8°. New 
York: D. Van Nostrand Co., 1908. 

Sindall, R. W. Paper technology. 2d ed., 270 pp., illus., tables, 8°. London: 
Chas. Griffin and Co., 1910. 

Stevens, Henry P. Paper mill chemist, 2S0 pp., 67 illus., 82 tables, 8°. Lon- 
don: Scott, Greenwood and Son, 1908. 

Sutermeister, Edwin. The soda process for cellulose manufacture; the consump- 
tion of caustic soda and its influence on yield and bleaching properties. (Presented 
at the Eighth International Congress of Applied Chemistry in New York, Sept. 11, 
1912.) In: Paper, IX (1912), (12), 15-16. 

Watt, Alexander. The art of papermaking. 3d ed., 260 pp., illus., 8°. Lon- 
don: Crosby, Lockwood and Son, 1907. 

EFFECTS OF CAUSTIC SODA AND WATER ON CELLULOSE. 

Cross (C. F.) and Bevan (E. J.). Cellulose. 3d ed., 328 pp., plates, djag., tables, 
8°. New York: Longmans, Green and Co., 1903. 

Cross (C. F.) and Bevan (E. J.). Researches on cellulose, 1895-1900, 2d ed., 180 
pp., tables, 8°; Researches on cellulose, 1900-1905, 184 pp., 8°; Researches on cellu- 
lose, 1905-1910, 8°. London: Longmans, Green and Co., 1907; 1906; 1912. 

Miller, O. Constitution of soda cellulose. In: Berichte, 41, 4297-4304; Chemi- 
cal Abstracts, 1909, 650. 



PRODUCING SODA PULP PEOM ASPEN. 63 

Miller-Moskan. The reaction of cellulose with sodium hydroxide. In: Be- 
nch te, 40, 4903-05; Chemical Abstracts, 1908, 1186. 

Schwalbe, Carl G. Die Chemie der Cellulose. Bibliographic 2 Bde., 8°. 
Berlin, 1910-1912. 

Schwalbe, Carl G. The cellulose problem. In: Paper, £ (1911), (4), 9. 

Schwalbe, Carl G., and Robinoff (Michael). Action of water and alkali upon 
cotton cellulose. In: Zeitschrift fur angew. Chemie, 24, 256-8; Chemical Abstracts, 
1911, 1838. 

Tauss, H. Verhalten von Holz und Cellulose gegen erhohte Temperatur und 
erhohten Druck bei Gegen wart von Wasser. In: Dingl. polyt. J., 273 (1889), 276- 
285. Abbreviated translation, "The behavior of wood and cellulose at high temper- 
atures in presence of water," in: Jour. Soc. Chem. Ind., 8 (1889), 913. 

Tauss, H. Verhalten von Holz und Cellulose gegen erhohte Temperatur und 
erhohten Druck bei Gegenwart von Natronlauge. In: Dingl. polyt. J., 276 (1890), 
411-428. Abbreviated translation, "The behavior of wood and cellulose at high tem- 
peratures and pressures in presence of caustic soda," in: Jour. Soc. Chem. Ind., 9 
(1890), 883. 

Viewig, W. The nature of alkali-cellulose, in: Papier Zeitung, 32 (1907), 130-131, 
174-175; Chemical Abstracts, 1907, 1320. 

Viewig, W. The action of cold caustic soda solutions on cellulose. In: Berichte, 
40, 3876-83; Jr. Soc. Chem. Ind., 26 (1907), 1157; Chemical Abstracts, 1908, 178. 

Viewig, W. Action of cold caustic soda on cellulose. In: Berichte, 41, 3269-75; 
Chemical Abstracts, 1908, 3403. 

o 



LIBRARY OF CONGRESS 



018 370 918 5 



